Oligohydramnios

Summary

Oligohydramnios is a condition in which there is less amniotic fluid than is expected for the gestational age. Etiologies include fetal conditions such as renal tract abnormalities, chromosomal abnormalities, and congenital infections, and maternal conditions such as placental insufficiency, late or postterm pregnancy, and premature rupture of the membranes. Oligohydramnios is suspected if abdominal girth and symphysis-fundal height are smaller than expected for gestational age, but ultrasound to measure the amniotic fluid index is required to confirm the diagnosis. Treatment varies depending on gestational age; amnioinfusion can be used to reduce complications in early pregnancy, whereas induction of labor may be appropriate in late pregnancy. Complications include intrauterine growth restriction, Potter sequence, and complications during labor and delivery, e.g., umbilical cord compression.

Definition

• Defined as an amniotic fluid volume (AFV) less than expected for gestational age, can arise from various causes, including reduced fetal urination due to kidney disease or obstruction and fluid loss from ruptured membranes.

Diagnosis

• Relies on ultrasound, with an amniotic fluid index (AFI) ≤5 cm or a single deepest pocket (SDP) <2 cm indicating oligohydramnios.

Etiology

• Maternal
  • Medical or obstetric conditions associated with uteroplacental insufficiency (eg, preeclampsia, chronic hypertension, collagen vascular disease, nephropathy, thrombophilia)
  • Medications (eg, angiotensin converting enzyme inhibitors, prostaglandin synthetase inhibitors [eg, NSAIDs], trastuzumab)
  • Diabetes insipidus (rare cases have presented with oligohydramnios that improve upon maternal treatment with desmopressin)
• Placental
  • Abruption
  • Twin to twin transfusion (ie, twin polyhydramnios-oligohydramnios sequence)
  • Placental thrombosis or infarction
• Fetal
  • Chromosomal abnormalities
  • Congenital abnormalities, especially those associated with impaired urine production or excretion
  • Growth restriction
  • Demise
  • Postterm pregnancy
  • Ruptured fetal membranes
  • Infection
• Idiopathic

Postdiagnostic Evaluation

• Upon diagnosis, a comprehensive evaluation including maternal history, physical examination for membrane rupture, and detailed sonography is recommended.
• Diagnostic amnioinfusion may be utilized for enhanced fetal visualization when oligohydramnios limits assessment. Additional diagnostic tools may be considered based on individual clinical scenarios.

Prognosis

The prognosis depends on the cause, severity, and gestational age at onset. While borderline/low normal AFV typically forecasts a favorable outcome, anhydramnios, especially in the second trimester, is associated with a significantly poorer prognosis. Adverse outcomes may stem from umbilical cord compression, uteroplacental insufficiency, or pulmonary hypoplasia in early-onset cases.

Prenatal Care

• Management of oligohydramnios involves addressing any underlying conditions and monitoring fetal well-being. Idiopathic cases may warrant weekly NSTs and SDP/AFI assessments, with biophysical profiles as an alternative.
• Fetal growth is monitored every three to four weeks, with Doppler velocimetry reserved for cases with fetal growth restriction.

Delivery Timing

For idiopathic oligohydramnios, delivery is suggested at 36+0 to 37+6 weeks to optimize outcomes, reflecting the uncertainty of benefits from prolonging the pregnancy to 39 weeks. The timing for conditions associated with oligohydramnios varies based on the specific diagnosis and clinical considerations.