Oligohydramnios Sequence
Oligohydramnios is defined as deficiency of amniotic fluid, i.e., decrease in the volume of amniotic fluid. It may result from decreased urinary production or excretion, or fluid loss from rupture of membranes. The incidence is estimated to be 0.5-8%
of all pregnancies.
GENETICS/BASIC DEFECTS
1. Associated maternal conditions a. Ureteroplacental insufficiency
i. Antiphospholipid antibodies ii. Chronic hypertension iii. Collagen vascular diseases
iv. Diabetic vasculopathy v. Maternal hypovolemia
vi. Preeclampsia/pregnancy-induced hypertension b. Drugs
i. Prostaglandin synthetase inhibitors ii. Angiotensin converting enzyme inhibitors c. Placental
i. Abruption
ii. Twin-to-twin transfusion d. Maternal hydration status 2. Associated fetal conditions
a. Renal malformations i. Bilateral agenesis ii. Bilateral cystic dysplasia
iii. Unilateral cystic dysplasia/agenesis iv. Meckel syndrome
v. Infantile polycystic kidneys vi. Renal tubular dysgenesis vii. Posterior urethral valves viii. Renal hypoplasia
ix. Horseshoe kidney b. Other congenital anomalies
i. Amniotic band syndrome ii. Branchio-oto-renal syndrome iii. Cystic hygroma
iv. Encephalocele
v. Endocardial fibroelastosis vi. Holoprosencephaly
vii. Hypophosphatasia (homozygous dominant form) viii. MURCS association
ix. Sacral agenesis (caudal regression) x. Sirenomelia
xi. VATER association xii. Others
c. Chromosome abnormalities i. Trisomy 13
ii. Trisomy 18
d. Twin-to-twin transfusion syndrome (‘stuck twin syn- drome’)
i. A complication of monochorionic diamniotic twinning
ii. One twin stucked because of severe oligohy- dramnios and compressed by the significant polyhydramnios associated with its co-twin iii. Perinatal mortality associated with severe oligo-
hydramnios/polyhydramnios sequence in a monochorionic twin pregnancy before 28 weeks:
70–100%
e. Intrauterine growth retardation f. Intrauterine fetal demise
g. Postmaturity possibly caused by a decline in placen- tal function
h. Rupture of membranes: the most common cause of oligohydramnios
i. Preterm ii. Prolonged iii. Idiopathic 3. Dynamic of amniotic fluid
a. Presence of amniotic fluid throughout gestation i. Enables normal development of the fetal respira-
tory, gastrointestinal, and urinary tracts and mus- culoskeletal system
ii. Continued fetal growth in a nonrestricted, sterile, and thermally controlled environment
iii. Amniotic fluid volume is gestational-age depe- ndent
b. Factors contributing to the formation and removal of amniotic fluid
i. Formation
a) Fetal urination b) Tracheal secretions
c) Intramembranous pathway including trans- fers between amniotic fluid and fetal blood perfusing the fetal surface of the placenta, fetal skin, and umbilical cord
d) Transmembranous pathway involving direct exchange across the fetal membranes between amniotic fluid and maternal blood within the uterus
ii. Removal: fetal swallowing c. Significance of oligohydramnios
i. A sign of potential fetal compromise
ii. Associated with an increased incidence of adverse perinatal morbidity and mortality, espe- cially in conjunction with the following:
a) Structural fetal anomalies b) Fetal growth restriction c) Post dates pregnancies d) Maternal disease
CLINICAL FEATURES
1. Consequences of severe fetal constraints secondary to early and prolonged oligohydramnios
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756 OLIGOHYDRAMNIOS SEQUENCE
a. Potter facies: associated with renal agenesis and any other cause of severe oligohydramnios
i. Hypertelorism
ii. Deep crease under the eyes iii. Epicanthal folds
iv. Flat nose v. Receding chin
vi. Low-set, aberrantly folded ears b. Lung hypoplasia
i. Respiratory insufficiency ii. Death
c. Limb positional anomalies i. Arthrogryposis ii. Spade-like hands iii. Talipes equinovarus
d. Intrauterine growth retardation: one of the most com- mon complications associated with sever oligohy- dramnios
2. Presence of fetal abnormalities in cases associated with severe oligohydramnios
a. 50.7% in the second trimester b. 22.1% in the third trimester c. Rate of aneuploidy: at least 4.4%
3. Correlation of the rate of survivors and the gestation when the severe oligohydramnios is diagnosed
a. 10.2% survivors in the second trimester b. 85.6% survivors in the third trimester
DIAGNOSTIC INVESTIGATIONS
1. Ultrasonography
a. Ultrasonographic modalities to assess oligohydramnios i. Single deepest vertical pocket (range: <0.5 cm to
<3 cm)
ii. Two-diameter pocket (vertical X horizontal
<15cm)
iii. Amniotic fluid index (AFI) (range: <5 cm to
<8 cm)
b. Defines oligohydramnios
i. Amniotic fluid index less than 7 cm
ii. Absence of a fluid pocket of 2–3 cm in depth c. Assesses fetal growth
d. Visualizes fetal kidneys, collecting system, and bladder e. Improves fetal structures by amnioinfusion
2. Chromosome analysis for aneuploidy 3. Autopsy for verification of etiology
GENETIC COUNSELING
1. Recurrence risk
a. Patient’s sib: depends on etiology b. Patient’s offspring: depends on etiology 2. Prenatal diagnosis
a. Ultrasonography b. Amniocentesis 3. Management
a. Maternal bed rest b. Maternal hydration
c. Serial amnioinfusions to prevent pulmonary hypopla- sia (complications including preterm labor, amnioni- tis, and perinatal deaths)
d. The risks of maintaining the fetus in utero must be weighed against the morbidities and mortalities of premature delivery.
REFERENCES
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OLIGOHYDRAMNIOS SEQUENCE 757
Fig. 1. An infant with renal agenesis and oligohydramnios showing characteristic Potter facies.
Fig. 2. Multicystic/dysplastic kidneys (arrows) causing oligohydramnios. Fig. 3. An infant with caudal regression showing Potter facies, anal atresia, arthrogryposis, and talipes equinovarus.
