Oligohydramnios

Definition

• Oligohydramnios is an amniotic fluid volume reduced for gestational age, defined sonographically by an amniotic fluid index of 5 cm or less or a deepest vertical pocket below 2 cm.
• It reflects an underlying disorder and is associated with increased neonatal morbidity.

Aetiopathogenesis

Aetiology and risk factors

• The most frequent causes are reduced fetal urine production, uteroplacental insufficiency and fluid loss after rupture of membranes; often no cause is found.
• Uteroplacental insufficiency arises, for example, in pre-eclampsia, chronic hypertension, placental abruption or thrombotic disorders; further causes are post-term pregnancy, growth restriction and fetal death.

Clinical features

Clinical features and complications

• Oligohydramnios itself usually causes no maternal symptoms other than a sense of reduced fetal movements; the uterus may be smaller than expected for gestational age.
• Complications include growth restriction, limb contractures and delayed or incomplete lung maturation if onset is early, reduced fetal tolerance of labour and fetal death; the risk depends on the amount of fluid and the cause.

Diagnosis

• Amniotic fluid volume is measured quantitatively by amniotic fluid index or deepest pocket; the amniotic fluid index tends to overdiagnose oligohydramnios.
• Investigation of the cause includes looking for prelabour rupture of membranes, a comprehensive ultrasound for malformations and placental causes, amniocentesis with karyotyping if malformations or aneuploidy are suggested, and umbilical artery Doppler in growth restriction.

Keep learning in the app

Further reading (selection)

1. StatPearls: Oligohydramnios (NCBI Bookshelf)
2. MSD Manual Professional Edition: Oligohydramnios

Cross-references