Polyhydramnios

Polyhydramnios is a condition of excess amniotic fluid surrounding the fetus during pregnancy. It is commonly defined by an amniotic fluid index (AFI) greater than 24 cm or a deepest vertical pocket greater than 8 cm on ultrasound, or by a total fetal fluid volume that is higher than normal for gestational age. The diagnosis is usually made during routine prenatal ultrasound.

The condition can arise from multiple mechanisms and is associated with a range of conditions. Approximately a majority of cases are idiopathic. Known associations include maternal diabetes with poor glycemic control, fetal anomalies that impair swallowing (such as anencephaly or esophageal/duodenal atresia), fetal conditions causing increased urine production, and twin-to-twin transfusion syndrome in multiple pregnancies. Infections and chromosomal abnormalities can also be linked to polyhydramnios. TTTS and multiple gestations carry specific risk profiles and management considerations.

Pathophysiology involves an imbalance between the production and removal of amniotic fluid. Hyperglycemia in the mother can lead to fetal hyperglycemia and polyuria, increasing fluid volume. Conversely, conditions that reduce fetal swallowing or absorption of fluid, or that increase fetal urine output due to other fetal or placental factors, can contribute to excess fluid.

Evaluation typically includes detailed ultrasound to assess fetal anatomy, growth, and amniotic fluid dynamics, along with screening for maternal diabetes and other potential underlying causes. Additional testing may be guided by findings, including fetal karyotype if anomalies are detected.

Management depends on severity and underlying cause. Mild cases with normal fetal course may require observation and regular monitoring. Moderate to severe polyhydramnios may necessitate targeted interventions, such as management of the underlying condition (e.g., optimizing maternal glucose control, treating TTTS) and, in select cases, procedures to reduce amniotic fluid. Prognosis varies with etiology and gestational age, with overall outcomes influenced by fetal anatomy, growth, and complication risk.