Oligohydramnios

A decreased amniotic fluid volume for gestational age (oligohydramnios), typically diagnosed by ultrasound as an amniotic fluid index (AFI) ≤5 cm or a single deepest vertical pocket (SDP) <2 cm, associated with increased fetal and perinatal morbidity and mortality.

Causes

• Premature rupture of membranes (PROM)

• Preterm premature rupture of membranes (PPROM)

• Fetal renal and urinary tract causes (reduced fetal urine production)

  • Bilateral renal agenesis

  • Polycystic kidney disease

  • Obstructive uropathy: Urethral valves, lower urinary tract obstruction

• Genetic and chromosomal causes

  • Trisomy 18

  • Trisomy 13

• Placental and fetal growth-related causes

  • Placental insufficiency

  • Intrauterine growth restriction (IUGR/FGR)

  • Post-term pregnancy (>42 weeks)

  • Fetal demise

  • Placental abruption

• Maternal and pregnancy-related causes

  • Preeclampsia

  • Maternal diabetes mellitus

  • Maternal dehydration

  • Severe maternal illness affecting uteroplacental perfusion

• Twin-to-twin transfusion syndrome (donor twin with oligohydramnios)

• Medications

  • ACE inhibitors

  • NSAIDs

• Fetal swallowing abnormalities