GROWTH, ENDOCRINE AND METABOLIC FUNCTION IN ADOLESCENTS BORN SMALL FOR GESTATIONAL AGE

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LITHUANIAN UNIVERSITY OF HEALTH SCIENCES MEDICAL ACADEMY

Indrė Petraitienė

GROWTH, ENDOCRINE

AND METABOLIC FUNCTION

IN ADOLESCENTS BORN SMALL

FOR GESTATIONAL AGE

Doctoral Dissertation

Medical and Health Sciences, Medicine (M 001)

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Dissertation has been prepared at the Department of Endocrinology of Medical Academy of Lithuanian University of Health Sciences during the period of 2010–2019.

Scientific Supervisor

Prof. Dr. Rasa Verkauskienė (Lithuanian University of Health Sciences, Medical and Health Sciences, Medicine – M 001).

Dissertation is defended at the Medical Research Council of the Lithuanian University of Health Sciences:

Chairperson

Prof. Dr. Žilvinas Dambrauskas (Lithuanian University of Health Sciences, Medical and Health Sciences, Medicine – M 001).

Members:

Prof. Dr. Saulius Paškauskas (Lithuanian University of Health Sciences, Medical and Health Sciences, Medicine – M 001);

Prof. Dr. Ričardas Radišauskas (Lithuanian University of Health Scien-ces, Medical and Health ScienScien-ces, Public Health – M 004);

Prof. Dr. Janina Tutkuvienė (Vilnius University, Medical and Health Sciences, Medicine – M 001);

Prof. Dr. Vallo Tillmann (University of Tartu, Medical and Health Sciences, Medicine – M 001).

Dissertation will be defended at the open session of the Medical Research Council at 11 a.m. on the 30th of August, 2019 in the Grand Auditorium of the Department of Endocrinology of the Hospital of Lithuanian University of Health Sciences Kauno klinikos.

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LIETUVOS SVEIKATOS MOKSLŲ UNIVERSITETAS MEDICINOS AKADEMIJA

Indrė Petraitienė

PAAUGLIŲ, GIMUSIŲ MAŽO GESTACIJOS

AMŽIUI ŪGIO IR/AR SVORIO, AUGIMAS

IR ENDOKRININĖS BEI METABOLINĖS

FUNKCIJOS

Daktaro disertacija Medicinos ir sveikatos mokslai,

medicina (M 001)

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Disertacija rengta 2010–2019 metais Lietuvos sveikatos mokslų universiteto Medicinos akademijos Endokrinologijos klinikoje.

Mokslinė vadovė

prof. dr. Rasa Verkauskienė (Lietuvos sveikatos mokslų universitetas, medicinos ir sveikatos mokslai, medicina – M 001).

Disertacija ginama Lietuvos sveikatos mokslų universiteto Medicinos mokslo krypties taryboje:

Pirmininkas

prof. dr. Žilvinas Dambrauskas (Lietuvos sveikatos mokslų universitetas, medicinos ir sveikatos mokslai, medicina – M 001).

Nariai:

prof. dr. Saulius Paškauskas (Lietuvos sveikatos mokslų universitetas, medicinos ir sveikatos mokslai, medicina – M 001);

prof. dr. Ričardas Radišauskas (Lietuvos sveikatos mokslų universitetas, medicinos ir sveikatos mokslai, visuomenės sveikata – M 004);

prof. dr. Janina Tutkuvienė (Vilniaus universitetas, medicinos ir svei-katos mokslai, medicina – M 001);

prof. dr. Vallo Tillmann (Tartu universitetas, medicinos ir sveikatos mokslai, medicina – M 001).

Disertacija ginama viešame Medicinos mokslo krypties tarybos posėdyje 2019 m. rugpjūčio 30 d. 11 val. Lietuvos sveikatos mokslų universiteto ligoninės Kauno klinikų Endokrinologijos klinikos Didžiojoje auditorijoje.

Disertacijos gynimo vietos adresas: Eivenių g. 2, LT-50162, Kaunas, Lietuva.

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ABBREVIATIONS

AGA – appropriate for gestational age ALT – alanine aminotransferase AST – aspartate aminotransferase BMD – bone mineral density BMI – body mass index BP – blood pressure CI – confidence interval CV – coefficient of variation

DHEAS – dehydroepiandrosterone sulphate DXA – dual-energy X-ray absorptiometry EF – ejection fraction

ELISA – enzyme-linked immunosorbent assay FAI – free androgen index

FSH – follicle-stimulating hormone FT4 – free thyroxine

GH – growth hormone

GnRH – gonadotropin-releasing hormone HDL – high-density lipoprotein cholesterol HPA axis – hypothalamic-pituitary-adrenal axis ICMA – immunochemiluminescent assay IGF-1 – insulin-like growth factor 1

IGFBP–3 – insulin-like growth factor binding protein 3 IR – insulin resistance

IRMA – immunoradiometric assay IUGR – intrauterine growth retardation IVS – interventricular septal thickness GH – growth hormone

LH – luteinizing hormone

LDL – low-density lipoprotein cholesterol LVEDD – left ventricular end-diastolic dimension LVM – left ventricular mass

LVMI – left ventricular mass index MS – metabolic syndrome OGTT – oral glucose tolerance test PCOS – polycystic ovarian syndrome PTH – parathyroid hormone

PW – posterior wall thickness RIA – radioimmune assay

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10 SEM – standard error of the mean SD – standard deviation

SDS – standard deviation score SGA – small for gestational age

SGACU+ – small for gestational age with catch-up growth SGACU– – small for gestational age without catch-up growth SHBG – sex hormone-binding globulin

TCh – total cholesterol TG – triglycerides

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INTRODUCTION

In recent years, most small for gestational age (SGA) newborns survive. However, growth in utero may have implications for growth and development throughout life. Small size at birth is related to an increased risk of perinatal morbidity and mortality. In addition, long-term con-sequences are also known in subjects born SGA. These individuals have been shown to be at a higher risk of short stature, alterations in pubertal development and metabolic consequences later in life. Insulin resistance (IR), dyslipidaemia, higher blood pressure (BP), overweight or obesity appear in younger age in SGA subjects compared with their peers born appropriate for gestational age (AGA).

Size at birth may be influenced by various maternal, placental and foetal factors; therefore, SGA newborns form a heterogeneous group with different aetiology and pathophysiology. Postnatal growth and development also depend on complexity of many internal and external factors, and it is still unclear which child born SGA is at an increased risk of later con-sequences and if there are early predictors to alert an increased risk. During adolescence, the human body undergoes dramatic changes: increases in growth hormone (GH) and sex steroid secretion lead to increased insulin resistance and accelerated somatic growth, as well as to changes in body composition. All these processes may unmask underlying disturbances in the metabolic function and the hormonal profile. Hopefully, better know-ledge of this condition and its natural course will allow suspecting unfa-vourable sequelae in individuals born SGA and recommending preventive measures.

Postnatal development and the metabolic status of SGA children were studied at the Endocrinology Department of Kaunas University of Medicine in 1998-2007, in collaboration with the Paediatric Research Center of Gote-borg University. In this study, small for gestational age weight was found to be related with short stature, increased risk of dyslipidaemia, glucose intolerance and insulin resistance. The current study is the continuation of this long-term follow-up, investigating the SGA cohort in adolescence and focusing on growth, pubertal development, insulin sensitivity, signs of ovarian hyperandrogenism, components of metabolic syndrome and bone mineral density in SGA-born adolescents.

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1. AIM AND OBJECTIVES OF THE STUDY

The aim of the study:

To evaluate the impact of size at birth and postnatal growth on anth-ropometry, pubertal development, body composition, metabolic and car-diovascular functions, hormonal profile and bone mineral density in ado-lescence.

The objectives:

1) to assess growth pattern and growth factors in children born SGA from birth to adolescence in comparison with children born AGA; 2) to compare pubertal development, gonadal sizes and sex hormones in

adolescents born SGA and AGA in relation to size at birth and early growth;

3) to explore components of metabolic syndrome (fat mass and its distribution, glucose metabolism, lipid profile and cardiovascular function) and cortisol secretion in adolescents born SGA and AGA in relation to early growth;

4) to assess the impact of vitamin D, PTH and calcium levels, pubertal development, size at birth and early growth on bone mineral density in children born SGA and AGA.

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2. NOVELTY OF THE STUDY

Although there are a number of studies analysing growth and metabolic profile in individuals born SGA, most are retrospective or of short duration. There are only a few prospective long-term follow-up cohorts of subjects born SGA worldwide, and most of them are focused on height growth and GH treatment safety and effectiveness in children born SGA. There are data on metabolic consequences in pre-pubertal children and adults born SGA in the literature, but there is a gap of studies during adolescence. Besides, the literature sources on pubertal development in individuals born SGA are mainly focused on precocious pubarche and the risk of polycystic ovarian syndrome (PCOS) in adult woman, but data on gonadal development and hormonal profile in adolescence are very scarce and controversial. To the best of our knowledge, there are only two cross-sectional studies describing sizes of internal genitalia in SGA-born adolescent girls at the beginning and at completion of pubertal development. Moreover, studies on metabolic and hormonal profile analyse either SGA subjects with catch-up growth (CU+) or without catch-up growth (CU–) or both groups combined; therefore, there is a lack of data comparing SGACU+ and SGACU– groups. To the best of our knowledge left ventricular mass index (LVMI) was evaluated for the first time in adolescents born SGA. Moreover, there are only a few publications on adrenal hormone secretion and, in particularly, on bone mineral density in children born SGA. To the best of our knowledge, this is the first study where bone mineral density in SGA adolescents was evaluated in relation to early growth.

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3. REVIEW OF LITERATURE

3.1. Incidence and definition of SGA

According to the definition used, about 2.3–10% of neonates are born small for gestational age [7, 91, 213]. In literature, the term small for

gesta-tional age (SGA) is used to describe neonates whose birth weight and/or

crown-heel length is below 10th, 5th, 3th percentile or −2 standard devia-tions (SD) below the mean according to sex and gestational age. It is recommended to use the cut-off level of −2 SD, as this group is likely to capture the majority of infants with impaired foetal growth and a highest risk of neonatal morbidity and mortality [150, 221].

Many literature sources use the term intrauterine growth retardation (IUGR) synonymously with the term SGA. However, these terms are different, and IUGR implies an underlying pathological process at some point of the foetal period and should be confirmed by several foetal growth assessments. The term SGA describes small size at birth according to gestational age and sex; therefore, specific to population birth weight and length reference data, accuracy in gestational dating and in measurement of length and weight at birth are needed [221].

3.2. Aetiology

Many factors may influence foetal growth and size at birth. The summary of these factors was presented by Sinead M. Bryan and Peter Hindmarsh [36] and is shown in Table 3.2.1. After the Second World War, it was no-ticed that intrauterine conditions might have implications for growth and development throughout life: individuals who were born after maternal undernutrition during pregnancy, especially during the third trimester of pregnancy, were more prone to poor glucose tolerance and insulin resistance [21, 237]. Epidemiological studies proved that being born SGA carries a higher risk of metabolic and cardiovascular consequences later in life, such as obesity, insulin resistance, dyslipidaemia and hypertension [18, 23, 50, 221]. It has been suggested that these effects may arise owing to foetal prog-ramming of hormone secretion and sensitivity facing stressful conditions in

utero [85]. The foetal adaptation allows surviving during the

nutrient-restricted period, but permanent changes are not appropriate for normal nutrition after birth and lead to long-term consequences later in life.

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Table 3.2.1. Factors associated with IUGR

Medical complications Preeclampsia

Acute or chronic hypertension Antepartum haemorrhage Severe chronic disease Severe chronic infections Systemic lupus erythematosus Antiphospholipid syndrome Anaemia

Malignancy

Abnormalities of the uterus Uterine fibroids

Maternal social conditions Malnutrition Low pregnancy BMI Low maternal weight gain Delivery at age < 16 or > 35 years Low socioeconomic status

Drug use Smoking

Alcohol Illicit drugs

Foetal problems Multiple births

Malformation

Chromosomal abnormalities Inborn errors of metabolism Intrauterine infections Environmental problems High altitude

Toxic substances Abnormalities of the placenta Reduced blood flow

Reduced area for exchange Infarcts Hematomas Partial abruption Adapted from Bryan and Hindmarsh [36].

3.3. Postnatal growth

3.3.1. Catch-up growth

It has been noticed that most individuals born SGA experience faster growth in weight and length than their peers. This phenomenon is called catch-up growth and is generally defined as growth velocity greater than the median for chronological age and gender [221]. Also, catch-up may be defined when corresponding to normal height and weight reference range for population (when reaching the third percentile or above −2 standard deviation (SD) of the mean) [221]. This definition is more convenient for clinical practice, but less predictive for later growth, as it does not

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incorporate target height, the genetic potential, which is the base for variant of individual growth.

It has been estimated that catch-up growth in SGA-born children is ex-perienced in the early postnatal period, typically during the first 6 months of life [4, 138]. Epidemiological studies have shown that rapid catch-up growth in terms of both weight and length during the first few months after birth is characteristically seen in approximately 90% of infants born SGA and is usually completed by the age of 2 years [100, 135, 221]. However, about 10% of children born SGA remain short at 2 years of age [4, 100, 135]. Catch-up growth may take longer, up to 4 years of age, in prematurely born infants [82, 100]. Insufficient catch-up growth is more common in very premature babies, infants who were short at birth and in some genetic syndromes (Silver-Russel, 3M) [50, 135]. However, it is still unclear, if catch-up growth may occur from childhood to adolescence.

3.3.2. Final height

As written above, it has been previously confirmed that absence of catch-up growth is related to short final height. However, there are data that despite catch-up growth in early life, final height is compromised in subjects born SGA compared with target height [149, 151, 152, 242]. One of the largest prospective studies has found that in SGA children without catch-up growth until 2 years of age the relative risk of short stature at 18 years of age is 5.2 if born light and 7.1 if born short for gestational age [4]. In this cohort, most infants born SGA experienced rapid postnatal catch-up growth during the first 6 months of life, and only 13.4% of them remained below −2SD at 1 year of age and 7.9% had a final height below −2SD according to Swedish growth standards [3, 4, 169]. It has been estimated that birth length and target height are the main predictors of final height in individuals born SGA [152, 169]. Nevertheless, postnatal growth depends on the complex of various endogenous and exogenous factors and there may be a few specific causes for compromised final height in subjects born SGA, such as abnormalities in growth hormone secretion and/or sensitivity, earlier onset of puberty or diminished pubertal growth spurt due to faster transition through puberty. These aspects will be reviewed later.

3.4. Growth hormone, IGF-1 and IGFBP3 secretion and sensitivity

Prenatal growth is mainly determined by insulin-like growth factor 1 (IGF-1), insulin-like growth factor 2 (IGF-2) and insulin secretion [92]. Several studies have found direct relationship of these hormones’

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concentrations in cord blood and size at birth [90, 153, 191, 258]. After birth, in most studies and in infants from our cohort, low levels of IGF-1 and insulin-like growth factor 1 binding protein 3 (IGFBP-3) were found [47, 61, 83, 153, 259]. In some of these studies, concomitantly higher levels of insulin-like growth factor 1 binding protein 1 (IGFBP-1) and insulin-like growth factor 1 binding protein 2 (IGFBP-2) in infants born SGA were described [47, 83]. In addition, in SGA infants, increased GH secretion was described [61, 153] and it was suggested that GH hypersecretion was one of the possible mechanisms of early postnatal catch-up growth [153]. On the other hand, decreased levels of IGF-1 and at the same time increased GH secretion suggest to some degree diminished sensitivity to GH in SGA neonates [221]. In older children born SGA, different GH/IGF axis profiles were found from diminished to normal GH and IGF-1 secretion [1, 31, 236, 254, 262, 273]. Studies show that most of the children born SGA have a normal response to GH stimulation tests [59]. However, higher basal GH secretion with higher peak frequency but lower peak amplitude and decreased IGF-1 concentrations were found in short children born SGA [31, 59]. It has been suggested that such changes in hormone secretion may reflect long-term disruption during foetal growth as similar hormonal profile is seen in adults after critical illness [60, 252]. In addition, a group from Chile revealed decreased pituitary sensitivity to IGF-1 in some SGA children without catch-up growth [215]. Only one study described the relationship of IGF-1 levels at birth with catch-up growth by 18 months [219], but most authors agree that in SGA-born individuals the status of the GH/IGF axis at birth or in early postnatal life do not predict later growth [153, 173]. In summary, impaired growth in SGA-born individuals could be related to changes in GH, IGF-1 and insulin secretion and sensitivity [32, 50, 150, 161, 178].

3.5. Pubertal development

3.5.1. Onset of puberty

Puberty is characterised by the development of secondary sexual charac-teristics, accelerated growth and behavioural changes [263]. Pubertal onset and progression are commonly assessed based on pubic hair development (pubarche) and development of genitalia (gonadarche). In girls, breast development (telarche) and cyclic bleeding (menarche) are also important markers of the pubertal process. The normal onset of puberty is defined as the development of secondary sexual characteristics between 8 and 13 years in girls and between 9 and 14 years in boys [96, 263]. Menarche usually

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begins 2 years after telarche, typically occurring between 12 and 13 years of age [95]. Variations in pubertal timing and progression are likely to be related to many factors, including ethnicity, genetic background, nutrition, coexisting disorders, medications, physical activity, socioeconomic status and other unknown factors [95, 263]. Gonadarche is mainly dependent on gonadal maturation and increased secretion of sex steroids due to stimu-lation of gonadotropins (luteinizing hormone (LH) and follicle stimulating hormone (FSH)). Pubarche is one of the expression of adrenarche, which is determined by an increase in adrenal androgen secretion and defined by changed sweat odour and development of axillary and pubic hair [263]. Precocious puberty is known to be related to advanced bone maturation, faster epiphyseal closing and compromised adult height [263].

3.5.1.1. Pubarche and DHEAS secretion

Previous studies have described the relationship of low birth weight with precocious pubarche, pronounced and precocious adrenarche, expressed by increased dehydroepiandrosterone sulphate (DHEAS) secretion [121, 122, 185, 248]. In one of the largest growth cohorts in the UK, “The Avon Longitudinal Study of Parents and Children” (ALSPAC), pronounced ad-renal androgen secretion was found in SGA children at 8 years of age, particularly in those with rapid postnatal weight gain [197]. Although most studies have found higher DHEAS levels in prepubertal and pubertal SGA children who had attained normal stature compared with those born AGA, no difference in DHEAS levels in those who did not experience catch up growth compared to AGA has been found [33, 54, 77, 114, 257]. The main limitation of most of these studies is that subjects were recruited from patients evaluated for precocious pubarche. However, not all studies have confirmed the relationship of being born SGA with increased adrenal androgen secretion [70]. Additionally, there is some evidence that enhanced pre- and peri-pubertal adrenal androgen secretion may disappear by early adulthood in full-term SGA-born subjects [246]. Moreover, even lower levels of DHEAS have been described in subjects born SGA compared with those born AGA in one study [211]. Thus, data are inconsistent and hypothesis of exaggerated adrenarche in SGA-born children need further confirmation.

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3.5.1.2. Gonadarche

There are a few studies where the onset of gonadarche has been eva-luated in children born SGA. In a large population-based study of postnatal growth of 3,650 healthy Swedish children, 87% of SGA children showed full catch-up growth and attained puberty at normal age. However, SGA children without catch-up growth throughout childhood reached puberty somewhat earlier than those with catch-up growth [2, 3, 136, 263]. Other studies have confirmed normal age at onset of puberty in SGA children, but it was significantly earlier than in AGA children in both sexes [149] or only in girls born SGA compared with their pairs born AGA [202]. Additionally, the study by Ingemar Persson showed that SGA children were on average 4 cm shorter at onset of puberty and, thus, at a risk of compromised final height [202]. Despite the fact that there may be some inaccuracies according to different evaluation of onset of puberty (in both Swedish studies, the onset of puberty was evaluated according to growth spurt), most authors agree that SGA children enter puberty at normal age, but relatively earlier than AGA.

3.5.2. Menarche

Several studies have explored the age at menarche in girls born SGA. Some longitudinal follow-up studies have not found any difference in the progression of puberty or age at menarche between girls born SGA and AGA [42, 151]. However, other authors have found normal but significantly earlier age at menarche in SGA girls compared with AGA [28, 81, 111, 145, 149, 202] or in girls whose birth weight was below the median compared with those with birth weight above the median [232].

3.5.3. Transition through puberty

In previous studies, earlier age at menarche suggested faster transition through puberty in SGA-born adolescent girls, which in turn may be related to diminished pubertal growth spurt and compromised final height. The study by Juliane Leger described similar total pubertal growth in SGA and AGA children [152], and a sufficient growth spurt in SGA-born adolescents was suggested. However, other studies have found some evidence that pubertal height gain may be smaller than expected in children born SGA: faster bone age maturation, earlier peak height velocity and similar onset of puberty but earlier age at menarche [148, 149] suggest faster transition through puberty in children born SGA.

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3.5.4. Sex hormones and gonadal sizes

In infancy, FSH hypersecretion has been found in boys and girls born SGA compared with those born AGA [95, 96, 123]. Data on gonadotropin secretion and the gonadal function in older boys and men born SGA are very scarce. Some authors have described increased prevalence of hypo-spadias and cryptorchidism in boys born SGA [105], decreased testosterone levels in post-pubertal SGA boys, and elevated levels of inhibin B or smaller testicular volume in men born SGA [8, 49]. However, other authors have not found differences in testicular size and morphology or secretion of sex steroids in boys and adult men born SGA compared with those born AGA [34, 88, 131, 142].

In post-menarcheal SGA girls, higher serum levels of FSH and lower estradiol concentrations have been found compared with those born AGA, and authors have suggested that this may be associated with gonadal resistance to gonadotropins [117]. Discordant findings were reported by Maria I. Hernandez et al.: at the beginning of puberty (Tanner stage 2 of breast development), SGA girls with BMI between 10th and 95th per-centiles had higher basal and gonadotropin-releasing hormone (GnRH) stimulated estradiol levels compared with AGA girls, whereas basal FSH and LH concentrations were similar in SGA and AGA children [94]. In the same cohort, 2 years later, FSH concentration was lower, but GnRH-sti-mulated LH and basal estradiol levels were higher in SGA children com-pared with AGA [95].

In addition, evidence exists that adolescent girls and women born SGA are more prone to anovulatory cycles and are at a higher risk of developing PCOS and subsequent infertility problems [110, 119, 120]. Besides, in adolescent girls born SGA with impaired growth prior to birth, a reduction in the size of internal genitalia and in the proportions of ovarian primordial follicles as well as ovarian hyperandrogenism and anovulation were re-ported in some studies [118, 245]. Different pathways of pathogenesis of PCOS are suggested. During puberty, adipose tissue dysfunction and increased levels of leptin are associated with hypersecretion of LH and the development of ovarian hyperandrogenism [57]. Moreover, it has been shown that individuals born SGA are more prone to hyperinsulinism, which in turn acts on ovarian theca through IGF-1 and results in increased levels of ovarian androgens. At the same time, hyperinsulinism is associated with a reduction in hepatic synthesis of sex hormone binding globulin (SHBG) and an increase in the levels of free fraction of circulating androgens in SGA women [57]. In addition, previous population studies have shown that serum androgen levels in adolescence correlate with those in adulthood, and that

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hyperandrogenism in puberty is associated with PCOS in adulthood [216, 269]. However, data on hormone status in girls born SGA are variable, and some studies have described similar androgen levels in girls born SGA and AGA [94].

There are only a few studies on gonadal morphology in SGA-born girls and women, and the results are controversial. According to data from Lourdes Ibanez et al., small size at birth might be associated with a reduced size of internal genitalia (ovarian and uterine) and a reduced ovarian fraction of primordial follicles in late adolescence [118]. In contrast, in the study by Hernandez et al., at the beginning of puberty, SGA girls had a slightly larger uterine size, ovarian volume and the number of follicles compared with AGA girls [94], but no significant differences in ultrasound measurements of internal genitalia were found between both groups after 2 years [94]. Thus, until now, data on sex hormone secretion and, in particular, on gonadal sizes are scarce and controversial.

3.6. Metabolic consequences

There is a large body of evidence suggesting that small size at birth is associated with a wide range of metabolic disorders later in life. However, until now, the pathogenesis of metabolic consequences, such as central adiposity, glucose intolerance, dyslipidaemia and hypertension, is not clear. Previously, it was thought that changes in glucose metabolism and the cardiovascular function arise due to rapid postnatal catch-up growth in weight and subsequent overweight and insulin resistance [27, 40, 157]. However, abnormalities in metabolic functions have been found in those individuals born SGA who remained lean [151, 224]. In addition, most studies analyse components of metabolic syndrome (MS) in adults or in children only at exact time in relation to size at birth, but not in relation to early postnatal growth. It is still unclear when these changes become no-ticeable and if there is any critical period to prevent or predict later con-sequences. Furthermore, some controversies exist on differences in the metabolic profile between SGACU– and SGACU+ individuals.

3.6.1. Overweight and fat mass distribution

In general population, pathogenesis of metabolic syndrome is mainly associated with an increased body mass index (BMI) and IR [98, 230]. It is known that being born SGA carries an increased risk of late metabolic consequences, particularly in those with catch-up growth [19, 20, 76, 109, 221, 223, 243], and rapid weight gain leading to excessive adiposity has

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been suggested to be the pathogenetic pathway [27, 40]. However, other studies have found changes in glucose or lipid metabolism and the cardio-vascular function in SGA children without catch-up growth [11, 225, 243] or in SGA children with catch-up growth even in the absence of overweight or obesity [113, 116, 227]. Usually, BMI and BMI standard deviation score (BMISDS) are used as surrogate markers of adiposity, although they do not reflect body adipose tissue compartmentalization. It has been proven that visceral, rather than general, fat component is responsible for a worse me-tabolic profile, and lipid accumulation in liver and muscle further predispose to insulin resistance and dyslipidaemia [98, 107, 164, 230]. Previous studies have found total fat mass to be comparable or even diminished in individuals born SGA or AGA [12, 52, 115, 116, 160], but with a tendency for increased visceral fat distribution in SGA infants, children and adults [6, 12, 29, 66, 73, 115, 127, 160, 193, 194, 227, 228, 240].

3.6.2. Adipokines

It has been estimated that changes in secretion and sensitivity of various adipokines, produced by adipose tissue, may impact insulin sensitivity and cardiovascular risk [230] even in absence of obesity [37, 175]. Evidence suggest that individuals born SGA are at a higher risk of adipocyte dysfunction; however, data are conflicting. Alterations in markers of adipose tissue dysfunction have been observed in individuals born SGA at birth, during childhood/adolescence and during the reproductive years [9, 48, 126, 236], regardless of the presence of obesity [115, 129]. However, some studies have not found changes in adipokine secretion or even higher adiponectin levels in SGA-born children and adults [75, 113]. Moreover, in one study, lower leptin levels have been described in SGA-born children [1]. However, most studies have confirmed the relationship of higher leptin and lower adiponectin levels with rapid postnatal weight gain [48, 129, 175], but data on adipokines in adolescents born SGA without catch-up growth are still lacking.

3.6.3. Glucose tolerance and insulin resistance

It was thought that in individuals born SGA insulin resistance was the main factor responsible for metabolic consequences later in life [32]. Re-duced insulin sensitivity has been reported in SGA children with postnatal catch-up growth as early as 1 year of age [116, 235], as well as in older pre-pubertal children and adults [177, 203, 250, 255, 256]. Besides, the relation-ship of rapid post-natal catch-up in weight with decreased insulin sensitivity

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from birth to 3 years of age has been noticed [32, 177]. Despite the fact that most studies have reported higher insulin resistance in children born SGA who experienced catch-up growth compared with their AGA-born pairs [76, 167, 192, 255], Paola Torre and colleagues did not find alterations in insulin sensitivity in SGA children with subsequent catch-up growth in BMI [247]. Moreover, Nicolette J. T. Arends and colleagues described reduced insulin sensitivity in pre-pubertal children without catch-up growth [11].

Since the late 1980s, numerous epidemiological studies have demons-trated a strong association between small size at birth with impaired glucose tolerance and type 2 diabetes mellitus in later life [174]. Significantly higher 120-min post–load glycaemia in SGA children has been reported by other studies as well [214, 250]. However, not all studies have found changes in glucose metabolism in children and adolescents born SGA [247, 255]. Associations have been found between rapid weight and BMI gain and glucose intolerance, and insulin resistance has been thought to be responsible for changes in glucose metabolism [29, 32, 73, 194]. However, some authors have described higher post-load glycaemia without decreased sensitivity to insulin in 4-year-old children born SGA [179]. In addition, previous studies have underlined the risk of metabolic consequences mainly for those individuals born SGA who experience catch-up growth. However, some evidence exists that those without catch-up growth may also have troubles in glucose metabolism [11]. Thus, it is still unclear when disorders in glucose metabolism appear and if there are differences in glucose metabolism and insulin sensitivity in SGACU+ vs. SGACU– adolescents.

3.6.4. Lipid metabolism

Several studies have reported a worse lipid profile in SGA-born children and adults with increased triglyceride levels [20, 23, 106, 174, 214], whereas in some studies decreased HDL or increased total or LDL choles-terol have been described [17, 243, 250]. However, many authors have not found any significant association between the SGA status or catch-up growth and lipid profile in childhood [40, 62, 225, 235, 253], even with subsequent catch-up growth in BMI [247]. Thus, it is still unclear if there are any differences in the lipid profile in adolescents born SGA vs. adolescents born AGA and, if so, what is the main underlying cause.

3.6.5. Cardiovascular function

Several studies have found an association between small size at birth and the prevalence of elevated blood pressure later in adulthood [17, 20, 106].

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During childhood and adolescence, only a small effect of being born SGA on blood pressure has been found [50, 209, 225], but in most studies, hyper-tension has not been diagnosed in SGA-born children and adolescents [50]. In a recent study by Katsuyasu Kouda et al., a relatively low body fat, however, with a more centralised fat distribution, has been associated with higher blood pressure in adolescence [144] and, as described above, such fat mass distribution is characteristic of individuals born SGA [115, 227]. However, it is not clear whether alterations in cardiovascular parameters are typical for all adolescents born SGA irrespective of catch-up growth and if the early growth may predict the risk of alterations in the cardiovascular function. There are some studies, where significantly greater aortic or carotid intima-media thicknesses were found in SGA-born individuals in infancy [227–229]. However, to the best of our knowledge, this is the first study where cardiac ultrasound and sizes of left ventricle were evaluated in adolescents born SGA.

3.7. Cortisol secretion

It has been suggested that foetal programming of the hypothalamic-pituitary-adrenal (HPA) axis may be related to an increased risk of meta-bolic consequences later in life in individuals born SGA [50, 221]. Stressful conditions in utero could lead to a small birth size [22, 199], and alterations in cortisol secretion could be the pathogenetic pathway for impaired metabolism and an increased risk of metabolic syndrome [50, 163, 246]. A few study groups have found no differences in serum cortisol levels between SGA and AGA children and adults [197, 211, 246] or between short SGA and short AGA children [54]. In contrast, other studies have described an even lower morning cortisol level in individuals born SGA compared with those born AGA in infancy, before puberty and in adulthood [26, 218].

In addition, one study has described the relationship of the highest serum cortisol to cortisone ratio with the poorest catch-up growth in SGA-born children [244]. Finally, most studies analyse pre-pubertal children or only short SGA children. Therefore, data are very limited and controversial, and studies are difficult to compare because of different age groups, study po-pulations and methodologies.

Some but not all studies described the link between hyperactivation of HPA axis and components of metabolic syndrome, such as hypertension, glucose intolerance and central adiposity [10, 79, 201, 217]. Therefore, we hypothesized that together with other components of metabolic syndrome, there is hyperactivation in cortisol secretion in adolescents born SGA.

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3.8. Bone mineral density

Data on bone mineral density in individuals born SGA are scarce. In infants born SGA, at birth and at 6 months of life, lower bone mineral content and decreased gain in bone mineral content during this period were described in a previous study by Monique Van de Lagemaat et al. [251]. In this study, at 6 months of age, lower bone accretion in SGA infants was found to be independent of body size, and authors concluded that prenatal conditions for bone accretion cannot be replicated post-natally [251]. Accordingly, in some studies in adolescents and adults, direct relationship of low birth weight with bone mineral density (BMD) has been found [16, 168]. However, not all studies have confirmed these findings. In a Dutch study, the main factors related to BMD in adulthood were weight gain during childhood, current weight, lean mass and fat mass, but there was no relation to size at birth [159]. Furthermore, in some studies SGA-born individuals have been suggested to have an alteration in leptin secretion and sensitivity, which is known to be closely related to bone mineralisation and remodelling [130, 171]. Since peak bone mass accrual occurs during adolescence [99, 171], bone mineral density in adolescents born SGA needs further investigation.

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4 . METHODS

4.1. Study design and population

This study is a continuation of the prospective long-term follow-up case-control study.

The initial cohort was constructed in 1998–2000 in Kaunas. The study population included 2 groups of subjects: SGA newborns and their peers born AGA as controls. The control group was formed of consecutive AGA infants, matched for gestational age and gender and only in the case if their umbilical cord blood was available for hormonal analysis [260]. At birth, 121 SGA and 185 AGA newborns were included in the cohort. All the children in the present study were born between 32 and 42 weeks of gesta-tion. In children born SGA, birth weight and/or length were below –2 SDS of the mean according to sex and gestational age according to Swedish reference data, because the initial study was a part of a joint Swedish-Brazilian-Lithuanian research project [187, 260]. Weight and length at birth in AGA newborns were between –2 and +2 SDS [187]. Infants were mea-sured within 24 hours after birth and the blood samples for IGF-1, IGFBP-3 and leptin concentrations were taken from the umbilical cord. Subsequently, the children were examined at 1, 2, 5, 12, 18 and 24 months after birth [260, 261].

The flowchart of the prospective long-term follow-up is presented in Fig. 4.1.1.

At 6–8 years (mean age, 6.3±0.07 years), 55 SGA and 103 AGA children from the initial cohort were investigated [249]. The subjects underwent anthropometric measurements, oral glucose tolerance test (OGTT), and lipid profile and hormones levels (insulin, IGF-1, IGFBP-3, leptin and adipo-nectin concentrations) were evaluated [249].

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Fig. 4.1.1. The flowchart of the prospective long-term follow-up.

Data at birth, early postnatal growth and data at 6 years adapted from Rasa Verkauskienė [260] and Margarita Valūnienė [249] (AGA, appropriate for gestational age; DXA, dual-energy X-ray absorptiometry; OGTT, oral glucose tolerance test; SGA, small

for gestational age).

Length/height and weight growth from birth to 6 years of age are pre-sented in Fig. 4.1.2. There was no difference in proportion of SGACU– chil-dren in total SGA group at 2 and 6 years (11.5% vs 12.7%, p=0.317).

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Fig. 4.1.2. Change in heightSDS and weightSDS during early childhood

in children born appropriate for gestational age (AGA); children born SGA

with catch-up growth (SGACU+) and children born SGA without catch-up

growth (SGACU–).

Data adapted from Verkauskienė and Valūnienė doctoral thesis [249, 260].

The present study population, investigated by the author of dissertation, included 102 adolescents (47 born SGA [24 boys and 23 girls] and 55 born AGA [23 boys and 32 girls]) from the initial cohort. At the time of investigation, the children were between 11 and 14 years of age (mean age, 12.5±0.1 years), and the mean pubertal stages were as follows: pubic hair development, 2 (interquartile range, 2–3); gonadarche (stages according to Tanner for breast development in girls and genital stages in boys), 2 (interquartile range, 2–3); testicular volume in boys, 5 mL (interquartile range, 2–9 ml). Besides, 40% of the girls (N=22) were post-menarche.

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During long-term follow-up, 191 subjects were lost of follow-up (due to changed contact information) and another 13 refused further investigation. However, during the last investigation the number of participants exceeded the smallest calculated sample size – 45. In addition, there was no difference in size at birth, mother’s age at delivery or hormone concentrations in the cord blood in the subjects who took part in the last investigation in adolescence compared with those who did not (Table 4.1.1).

Table 4.1.1. Birth data in adolescents evaluated at 11–14 years and those

lost of follow-up

Participated in

adolescence participated Do not value P

Gestational age (weeks) 39.0±0.13 39.0±0.11 0.904

Birth length (cm) 49.4±0.26 49.6±0.19 0.530

Birth weight (g) 3159±58 3145±46 0.847

BMI at birth (kg/m2) 12.7±0.15 12.6±0.12 0.606

Mothers age at delivery (years) 27.6±0.46 27.0±0.36 0.334

Mothers BMI before pregnancy (kg/m2) 22.3±0.35 22.4±0.30 0.845

IGF-1 (µg/L) 62.5±3.56 60.0±2.61 0.758

IGFBP3 (µg/L) 1502±80.5 1431±61.0 0.425

Leptin (µg/L) 6.4±0.71 5.8±0.37 0.780

4.2. Anthropometric measurements, hormonal profile

and instrumental examination

The current age of the child was recorded in decimals.

Anthropometric measurements. All anthropometric and blood pressure

measurements and assessment of pubertal development were made by the author of dissertation. Study children were measured wearing underwear and barefoot. Height was measured to the nearest 0.1 cm using a standard Harpenden wall-mounted stadiometer (Holtain, Ltd., Crosswell, UK), and weight was measured to the nearest 0.1 kg using Soehnle electric scales (Soehnle, Backnang, Germany). Length/height and weight measurements were converted to SDS according to Swedish birth weight, length and BMI references because SDS references for Lithuanian children were not available and in order to be able to compare previous data of this cohort. An algorithm based on the data from 800,000 healthy newborns born between 1990 and 1999 at a gestational age of 24–43 weeks was used from birth to 2 years of age [186, 261], combined with an algorithm for total height and

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weight up to 20 years of age [271]. BMI was calculated as a ratio of weight (kg) to height (m2) and converted to SDS [137].

Pubertal staging. Pubertal stage was assessed according to criteria of

Tanner [241]. In boys, development of genitalia and pubic hair were evaluated. In girls, breast and pubic hair development were evaluated. The girls’ self-reported age at menarche was recorded, and those who were pre-menarcheal at the latest investigation were contacted 4 years later to record their age at menarche (N=32).

Definition of catch-up growth. As height in adolescence is dependent on

onset of puberty, the children born SGA were assigned to the groups based on height before puberty: SGA children with a height above –2 SDS of the mean of the reference population according to sex and exact age during the investigation at 6 years of age were considered to be SGACU+ [186, 271]; SGA children with a height below –2 SDS of the mean at 6 years of age were considered to be SGACU–.

Skinfold thickness was measured to the nearest 0.1 cm at the subscapular,

upper arm (triceps) and thigh area on the left-hand side using the Harpenden skinfold calliper. Two measurements were performed at each site, and the mean value was used for analysis. Limb skinfold thickness was calculated as the sum of skinfold thicknesses in the upper arm and thigh area.

Waist and hip circumferences were measured with a flexible

non-stretchable measuring tape to the nearest 0.1 cm. The waist circumference was measured in the middle between the imaginary lines connecting the lower edge of the ribs and the upper edge of the clubtails (crista iliaca

superior). The hip circumference was measured as the maximal

circum-ference over the buttocks (at the level of the great femoral trochanter). Every measurement was repeated twice, and the mean value used for analysis.

Cardiovascular parameters. Systolic and diastolic blood pressure (BP)

were measured in a quiet environment and in a seated position for at least 30 min using an automatic device with a cuff size appropriate for the arm circumference. The measurements were repeated twice 5 min apart, and the mean value was used for analysis.

BMD was determined by dual-energy X-ray absorptiometry (DXA)

(Hologic Discovery). The software calculated the results of lumbar bone mi-neral mass (g), the measured area (cm2), BMD (g/cm2) and BMD Z-score, and the last two were used for comparison. The software estimates sex, age, height and weight of the subject. The device irradiation dose was 0.2 μSv.

Fat mass percent was measured using bioelectric impedance (Jawon

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muscle mass and their absolute values in kilograms were used for com-parison.

The ultrasound of internal genitalia was performed with an abdominal

sensor by a single skilled gynaecologist. The measurements were performed if there was no dominating follicle. The volume of each ovary was determined by measuring the three widest perpendicular diameters and applying the formula for the volume of an ellipsoid: [L×W×D×π]/6; the average volumes of both ovaries were used for comparison [212]. The uterine volume was determined by measuring the longitudinal dimension in sagittal section from the highest fundal point in the midline to the corresponding midline cervical point, the anteroposterior diameter at the widest fundal dimension and widest transverse diameters. The same formula for the volume of an ellipsoid was used to calculate uterine volume.

Echocardiography was performed in two-dimensional-guided M-mode

by two skilled cardiologists. Left ventricular end-diastolic dimension (LVEDD), posterior wall thickness (PW), interventricular septal thickness (IVS) and ejection fraction (EF) were measured.

Left ventricular mass (LVM) was calculated using the Devereux equa-tion from echocardiographic measurements: LVM (g)=1,04[(IVS+PW+ LVEDD)3–LVEDD3] [63]. LVM index (LVMI) was obtained according to the equation by Stephen R. Daniels and Giovanni De Simone, using for-mula: LVMI=LVM/height (cm)2.7 [56, 58].

4.3. Laboratory measurements and evaluation

Venous blood samples for hormones measurements were taken once between 08:00 and 09:00 am after overnight fasting, centrifuged within 1 hour and stored at –20°C until hormone concentrations were determined. At the same time, OGTT was performed: blood samples for glycaemia and insulin assessment were drawn while fasting, 30 min and 2 h after glucose (1.75 g/kg, max 75 g) load. Venous blood samples for biochemical analysis (plasma glucose concentration, lipid profile, liver enzymes, calcium and phosphate concentrations) were delivered to the laboratory immediately and were analysed within 2 hours after collection.

Plasma glucose concentration was measured using the oxygen coefficient

method by means of biochemical analyser “Synchron” (USA). Fasting lipid profile, liver enzymes alanine aminotransferase (ALT) and aspartate amino-transferase (AST) were assessed by means of the standard procedure in a biochemical laboratory by enzyme-linked immunosorbent assay (ELISA) kit “Instrumentation Laboratory” (USA). Intra-/inter- assay coefficient of va-riation (CV) for total cholesterol (TCh), low-density lipoprotein cholesterol

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(LDL), high-density lipoprotein cholesterol (HDL), triglycerides (TG), ALT and AST were 1.8/1.8%, 1.2/2.6%, 3.2/2.0%, 1.2/2.3%, 1.8/2.0% and 1.5/2.0%, respectively. Calcium and phosphate concentrations were as-sessed using ion-selective or acidic ammonium molybdate methods (Beck-man Coulter, USA) by means of the standard procedure in a biochemical laboratory.

Hormone concentrations were measured in a certified clinical laboratory by a commercially available immunoradiometric assay (IRMA) or radioim-mune assay (RIA) reagent kits or 1–two-step immunochemiluminescent assay (ICMA). Methods, intra-/inter-assay CV and producers of reagents kits are presented in Table 4.3.1.

Table 4.3.1. Methods, intra-/inter-assay CV and producers of reagents kits

Parameter Detection _limit Intra-/inter-assay _{CV (%)} Method Producer

Insulin 1.0 mIU/L 1.9/6.3% IRMA DIAsorce, Belgium

IGF-1 3.4 µg/L 4.3/6.5 RIA DIAsorce, Belgium

IGFBP-3 17.3 µg/L 3.3/4.4 IRMA DIAsorce, Belgium

Leptin 0.1 µg/L 4.8/5.3 RIA DIAsorce, Belgium

Adiponectin 0.78 µg/L 8.5/8.9 RIA Millipore, USA

DHEAS 0.064 μmol/L 4.6/5.8 RIA IZOTOP, Hungary

Cortisol 2.4 nmol/L 7.7/4.7 RIA DIAsource, Belgium

LH 0.2 U/L 6.7/3.7 IRMA IZOTOP, Hungary

FSH 0.1 U/L 2.0/4.4 IRMA IZOTOP, Hungary

Estradiol 7.3 pmol/L 5.9/10.1 RIA DIAsorce, Belgium

Testosterone 0.2 nmol/L 4.6/6.2 RIA DIAsorce, Belgium

SHBG 0.3 nmol/L 3.8/4.4 IRMA Zentech, Belgium

FT4 0.7 pmol/L 3.1/5.8 RIA IZOTOP, Hungary

TSH 0.009 mIU/L 1.8/4.1 IRMA IZOTOP, Hungary

Vitamin D 7.03 nmol/L 4.7/6.4 ELISA DIAsource, Belgium

PTH 1.0 ng/L 3.6/4.2 ICMA TOSOH, Japan

DHEAS, dehydroepiandrosterone sulphate; FSH, follicle-stimulating hormone;

FT4, free thyroxine; ICMA, immunochemiluminescent assay; IGF-1, insulin-like growth factor 1; IGFBP-3, insulin-like growth factor binding protein 3; IRMA, immunoradiometric assay; LH, luteinizing hormone; PTH, parathyroid hormone; RIA, radioimmune assay; SHBG, sex hormone-binding globulin; TSH, thyroid-stimulating hormone.

Insulin resistance was evaluated using the homeostasis model assessment of insulin resistance index (HOMA-IR, calculated using the formula: [fasting

plasma glycaemia (mmol/L) × fasting plasma insulin (mU/L)]/22.5) [234].

Free androgen index (FAI) was calculated using the following formula:

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girls, blood samples were taken in the follicular phase of the menstrual cycle or at least 2 months of secondary amenorrhea and if there was no domi-nating follicle. No girl received any hormonal treatment prior to the study.

4.4. Statistical analyses

Sample size (n) was calculated using formula n = Zp2×p×(1–p)/∆2, where Zp – normal variety (1.96); p – expected proportion of SGA (3% according to literature); ∆ – absolute error (0.05) [184]. The calculated sample size was 45 and the number of participants in our study exceeded the smallest sample size.

The distribution of quantitative variables was tested for normality using the Kolmogorov–Smirnov test. Skewed parameters were log-transformed before analyses to ensure Gaussian distribution. The data for normally distributed variables are presented as mean and standard error of the mean (SEM); rank variables are presented as median and range. The study cha-racteristics were compared using independent-sample t tests for continuous variables and the χ2

test for binary and rank variables. Between-group com-parisons for continuous variables were made using univariate general linear models with least square difference adjustment; all the values were adjusted for current age, pubertal stage, BMISDS and sex (except analyses divided by sex); the values for blood pressure analyses and sizes of internal genitalia were also adjusted for current height. LVMI analysis was additionally adjusted for systolic BP. When non-homogenous in sample size groups were compared, significance was additionally verified by reducing the larger group by random selection. Partial correlation tests and Pearson correlation coefficients were used to analyse the relationship of parameters in adoles-cence with size at birth, and early growth (in every measured interval).

Hierarchical multiple regression models using standardised coefficients were used to explain the variation and to evaluate associations between parameters during adolescence and perinatal and postnatal factors, after controlling for sex, age, pubertal stage and BMISDS. A p value of <0.05 was considered statistically significant. Statistical analyses were performed using the SPSS statistical software package for Windows (version 20.0).

4.5. Statement of ethics

The study was approved by the Regional Biomedical Research Ethics Committee at the Lithuanian University of Health Sciences in Kaunas (No. BE-2-42, 14.06.2011), and informed written consent was obtained from all the parents prior to the study.

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5. RESULTS

5.1. Study characteristics

In our cohort, 31 subjects were defined as SGA according to birth length and 46 according to birth weight. In total, 30 children were defined as SGA according to both parameters (birth length and weight). Of the 47 children born SGA, 7 (14.9%; 3 boys, 4 girls) did not experience catch-up growth (SGACU–): their height was below −2 SDS until late childhood (6 years of age); the remaining 40 children born SGA experienced spontaneous catch-up growth (SGACU+, height above −2 SDS at the same age). Anthropometric measurements in AGA, total SGA, SGACU– and SGACU+ groups are pre-sented in Table 5.1.1.

At the time of the study, SGACU– children were significantly shorter and lighter than SGACU+ children and children born AGA. BMISDS was also lower in SGACU– children compared with SGACU+ and AGA children; ho-wever, the waist-to-height ratio was higher in SGACU– adolescents compared with SGACU+ and AGA adolescents. At the time of the study, SGACU+ children were also shorter than the children born AGA, but there was no significant difference in weightSDS, BMISDS and waist-to-height ratio between SGACU+ and AGA adolescents.

Pubertal stages for study children are presented in Table 5.1.2.

As the study children were in different pubertal stages, we compared maturation/biological age, expressed by testicular volume in boys and breast development stages in girls. When separated by sex, there was no difference in biological age between SGA and AGA children (all SGA vs AGA, boys: p=0.120; girls: p=0.694). Besides, there was no difference in testicular size between SGACU– and SGACU+ boys (p=0.481, Fig. 5.1.1). The stages of breast development in SGACU+ and AGA girls were similar (p=0.132), with most girls being in the third stage of breast development according to Tanner (Fig. 5.1.2). However, 2 of 4 SGACU– girls were pre-pubertal (in the first stage for breast and pubic hair development) (p=0.005 compared with SGACU+ girls (0 out of 20); p=0.034 compared with AGA girls (3 of 31).

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T abl e 5.1 .1 . D em ogr aphi c and ant hr opom et ri c ch a ra ct er is ti cs of t he s tudy popul at ion (m ea n ± S E M, if not i ndi cat ed ot he rw is e) AG A (N =55) SGA _(N=47) P va lue a SGA CU –-(N =7) P va lue b SGA CU + (N =40) P va lue c P va lue d 1 2 3 4 5 6 7 8 9 Gen d er , b o y s/ g ir ls (% ) * 43. 6/ 56. 4 51. 1/ 48. 9 0. 55 1 42. 9/ 57. 1 0. 96 9 52. 5/ 47. 5 0. 40 0 0. 64 2 At b ir th Ges tat io n al a ge ( week s) 39. 2± 0 .2 38. 7± 0 .3 0 .1 34 37. 7± 1. 1 0 .0 52 38. 9± 0 .2 0. 34 0 0. 07 7 We ig h tSDS − 0. 0 8± 0. 1 3 − 3. 0 9± 0. 1 6 < 0. 00 1 − 4. 1 9± 0. 7 3 < 0. 00 1 − 2. 8 9± 0. 1 3 < 0. 00 1 0. 00 2 L en gt hSDS − 0. 0 7± 0. 1 6 − 2. 6 2± 0. 2 4 < 0. 00 1 − 4. 6 0± 1. 0 < 0. 00 1 − 2. 2 7± 0. 1 8 < 0. 00 1 < 0. 00 1 L ean ma ssS DS − 0. 0 4± 0. 1 4 − 1. 8 2± 0. 1 7 < 0. 00 1 − 1. 8 9± 0. 8 6 < 0. 00 1 − 1. 8 0± 0. 1 4 < 0. 00 1 0. 85 1 BM I (k g/ m 2 ) 13. 7± 0. 2 11. 1± 0 .2 < 0. 00 1 10. 8± 0. 7 < 0. 00 1 11. 1± 0 .16 < 0. 00 1 0. 46 5 P onde ra l ind ex ( kg/ m 3 ) 2. 70± 0 .03 2. 37± 0 .03 < 0. 00 1 2. 52 ± 0. 1 2 0. 05 1 2. 35± 0 .03 < 0. 00 1 0. 09 4 Head ci rcu m fer en ce (c m ) 35. 2± 0 .2 33. 1± 0 .2 < 0. 00 1 33. 7± 0. 4 0. 00 6 33. 1 ± 0. 2 < 0. 00 1 0. 22 2 At 6 ye a rs of a ge A ge ( y ear s) 6. 5± 0. 1 6. 2± 0. 1 0. 01 9 6 .3± 0 .3 0. 49 1 6 .2 ± 0 .1 0. 14 0 0. 40 2 Hei g h t (c m ) 120. 7± 1. 0 114. 2± 1. 2 < 0. 00 1 104. 7± 2 .4 < 0. 00 1 116. 7 ± 0 .9 0. 00 6 < 0. 00 1 Hei g h tSDS − 0. 0 3± 0. 1 5 − 0. 9 4± 0. 2 5 0. 00 4 − 3 .05 ± 0 .46 < 0. 00 1 − 0 .39 ± 0 .18 0. 15 3 < 0. 00 1 We ig h t (kg ) 22. 5± 0 .6 19. 1± 0 .5 < 0. 00 1 15. 5± 1. 1 < 0. 00 1 20. 1 ± 0. 5 0. 00 2 0. 00 1 We ig h tSDS − 0. 1 7± 0. 1 7 − 1. 2 7± 0. 2 5 < 0. 00 1 − 3 .11 ± 0 .54 < 0. 00 1 − 0 .79 ± 0 .19 0. 02 3 < 0. 00 1 BM I (k g/ m 2 ) 15. 4± 0 .3 14. 6± 0 .2 0. 02 8 13. 9± 0. 5 0. 02 6 14. 7 ± 0. 3 0. 09 2 0. 23 5 BM ISDS − 0. 2 7± 0. 1 9 − 1. 0 2± 0. 2 4 0. 01 7 − 1 .63 ± 0 .55 0. 01 1 − 0 .86 ± 0 .26 0. 07 2 0. 15 4 Head ci rcu m fer en ce (c m ) 53. 0± 0 .3 51. 3± 0 .3 < 0. 00 1 50. 1± 0. 5 < 0. 00 1 51. 6 ± 0. 3 0. 00 1 0. 02 4 S u b scap u lar s k inf ol d t h ick n es s (m m )* * 9. 62± 0 .56 7. 90± 0 .59 0. 04 7 7. 66 ± 1. 2 7 0. 17 1 7. 97 ± 0. 6 6 0. 07 1 0. 83 0 Li m b s k in fo ld t h ick n es s (mm) * * 29. 1± 1 .0 25. 4± 1 .1 0. 02 0 23. 8± 2. 3 0. 04 1 25. 8 ± 1. 2 0. 05 0 0. 42 4 Wa is t ci rcu m fer en ce ( c m) * * 53. 4± 0 .6 53. 7± 0 .7 0. 75 1 50. 0± 1. 4 0. 03 0 54. 7 ± 0. 7 0. 19 4 0. 00 3

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T abl e 5. 1.1 co nt in ue d ₁ 2 3 4 5 6 7 8 9 Wa is t to he ig ht r at io * * 0. 45± 0 .01 0. 47± 0 .01 0. 00 2 0. 48 ± 0. 0 1 0. 01 0 0. 47 ± 0. 0 1 0. 00 9 0. 37 6 W ai st t o h ip r at io * * 0. 89± 0 .01 0. 90± 0 .01 0. 40 2 0. 91 ± 0. 0 2 0. 24 9 0. 89 ± 0. 0 1 0. 59 7 0. 41 6 At t h e ti m e of i n v es ti g at io n A ge ( y ear s) 12. 6± 0. 1 12. 3± 0. 1 0. 09 6 11. 6 ± 0. 3 9 0. 00 9 12. 4 ± 0. 1 5 0. 35 6 0. 03 3 Hei g h t (c m ) 158. 8± 1 .0 152. 1± 1 .5 < 0. 00 1 137. 6 ± 4 .42 < 0. 00 1 154. 6 ± 1 .24 0. 01 6 < 0. 00 1 Hei g h tSDS 0. 36 ± 0. 1 3 − 0 .38 ± 0 .19 0. 00 1 – 2 .3 0 ± 0 .67 < 0. 00 1 – 0. 1 0± 0. 1 5 0. 03 8 < 0. 00 1 We ig h t (kg ) 49. 3± 1. 5 42. 2± 1. 4 0. 00 1 29. 2 ± 2. 6 7 < 0. 00 1 44. 5 ± 1. 2 8 0. 02 1 < 0. 00 1 We ig h tSDS 0. 59 ± 0. 2 1 − 0 .36 ± 0 .25 0. 00 4 − 2 .53 ± 0 .67 < 0. 00 1 0. 02 ± 0. 2 3 0. 07 4 < 0. 00 1 BM I (k g/ m 2 ) 19. 4± 0. 5 18. 0± 0. 4 0. 03 2 15. 2 ± 0. 6 2 0. 00 1 18. 5 ± 0. 4 2 0. 16 4 0. 01 1 BM ISDS 0. 31 ± 0. 1 7 − 0 .17 ± 0 .20 0. 06 9 − 1 .52 ± 0 .49 0. 00 1 0. 06 ± 0. 2 0 0. 35 3 0. 00 3 Head ci rcu m fer en ce (c m ) 55. 4± 0. 3 53. 9± 0. 3 < 0. 00 1 51. 3 ± 0. 7 0. 00 1 54. 2 ± 0. 3 0. 00 2 < 0. 00 1 S u b scap u lar s k inf ol d t h ick n es s (m m )* * * 9 .0± 0 .5 11. 1± 0. 6 0. 00 4 13. 1 ± 1. 8 0. 04 3 10. 9 ± 0. 6 0. 04 1 0. 25 4 Li m b s k in fo ld t h ick n es s (mm) * ** 28. 1± 1. 2 31. 2± 1. 3 0. 08 9 58. 6 ± 2. 3 0. 88 7 57. 2 ± 0. 8 0. 82 9 0. 82 9 Wa is t ci rcu m fer en ce ( c m) * ** 66. 3± 0. 4 66. 1± 0. 5 0. 75 3 66. 8 ± 1. 4 0. 76 2 66. 0 ± 0. 5 0. 78 6 0. 85 3 Wa is t to he ig ht r at io *** 0. 42 ± 0. 0 1 0. 43 ± 0. 0 1 0. 01 3 0. 45 ± 0. 0 1 < 0. 00 1 0. 43 ± 0. 0 1 0. 07 1 0. 00 3 W ai st t o h ip r at io * * * 0. 80 ± 0. 0 1 0. 80 ± 0. 0 1 0. 77 4 0. 81 ± 0. 0 2 0. 80 2 0. 80 ± 0. 0 1 0. 80 1 0. 88 8 M us cl e m as s ( kg )*** 37. 1 ± 0. 5 36. 5 ± 0. 8 0. 47 7 27. 5 ± 3. 4 0. 00 7 36. 8 ± 0. 7 0. 72 3 0. 00 9 M u scl e m as s ( % )* * * 77. 5 ± 0. 5 76. 5 ± 0. 8 0. 26 6 71. 0 ± 3. 3 0. 05 0 76. 8 ± 0. 8 0. 41 5 0. 09 1 F at m as s ( k g )** * 8 .2 ± 0 .4 8 .5 ± 0 .5 0. 62 9 11. 8 ± 1 .3 0. 00 9 8 .0 ± 0 .5 0. 87 2 0. 00 8 F at m as s (% )* * * 16. 0 ± 0. 4 9 17. 3 ± 0. 6 1 0. 17 0 21. 4 ± 1. 6 0. 00 2 16. 7 ± 0. 6 0. 37 4 0. 00 9 Dat a at b ir th an d 6 y ear s ad ap ted f ro m Ver k au sk ien e an d Val u n ien e doc tor al t he si s [24 9, 26 0] . a S GA v s AGA; b S GA CU – v s AG A; c S GA CU + v s AGA; d S GA CU – vs S G ACU + . AG A, a ppr opr ia te f or g es ta ti o n ag e; B M I, bod y ma ss i nde x ; B M I, bod y ma ss i nde x ; BM ISDS , body ma ss i nde x s tan d ar d d ev ia ti o n s co re; S GA, s ma ll for g es tat io n al ag e. S DS v al u es f or l en g th , wei g h t and B MI wer e cal cu lat ed acco rd in g t o S wed is h gr o w th r ef er en ces [ 13 7, 1 86, 271 ]. * P va lu e of χ 2 t es t was u sed f or c om pa ri son b et ween S GA a n d AGA c hi ldr en. ** D at a are p re sen ted as es ti m at ed m ean a nd S EM, ad ju st ed f or s ex, age at i n v es ti g at io n an d B MI S DS . *** Dat a are p res en ted as es ti m at ed m ean an d S EM, ad ju st ed f or s ex, ag e, B MI S DS an d pu b er tal s tag e.

GROWTH, ENDOCRINE AND METABOLIC FUNCTION IN ADOLESCENTS BORN SMALL FOR GESTATIONAL AGE

Indrė Petraitienė