Polyhydramnios

Introduction

• Description: Polyhydramnios (also known as hydramnios) is an abnormal increase in the amount of amniotic fluid surrounding the fetus. This diagnosis is generally reserved for volumes greater than 2 L and amniotic fluid index greater than 24–25 cm. (At term, there should be approximately 800 mL of amniotic fluid present). This fluid may gradually accumulate over time (chronic hydramnios) or acutely over the course of several days (more common in early pregnancy).

• Prevalence: In 0.7%–2% of pregnancies, some increase in amniotic fluid is observed during pregnancy (80% mild; 5% severe).

• Predominant Age: Reproductive age.

• Genetics: No genetic pattern.

Etiology and Pathogenesis

• Causes: Idiopathic (40%), maternal diabetes (25%), multiple gestation, fetal anemia, fetal anomalies (50% of patients with severe hydramnios: central nervous system, gastrointestinal tract, chromosomal [trisomies 18 and 21]).

• Risk Factors: Fetal anomalies that impair swallowing or alter urine production, multiple gestation (twin–twin transfusion), maternal diabetes, erythroblastosis.

Signs and Symptoms

• Uterine size larger than normal for stage of pregnancy

• Increased amniotic fluid measured by ultrasonography (amniotic fluid index >24–25 cm)

• Dyspnea (especially when supine)

• Lower-extremity and vulvar edema

• Premature labor

• Difficulty palpating fetal parts or hearing fetal heart tones

Diagnostic Approach