Does polyhydramnios affect the fetus?

The fluid filling the amniotic cavity is called amniotic fluid. Its origin, volume, and composition vary with gestational age. During early pregnancy, amniotic fluid primarily consists of dialysate derived from maternal serum crossing the placenta into the amniotic cavity, with a small amount seeping from the placental and umbilical cord surfaces. Once fetal circulation is established, water and small molecules from the fetal body can pass through the non-keratinized fetal skin into the amniotic cavity, contributing to the amniotic fluid.

What impact does polyhydramnios have on the fetus?

1. Acute polyhydramnios

Amniotic fluid originates mainly from plasma components across the placenta, fetal urine, respiratory and gastrointestinal secretions, the umbilical cord surface, and the placental surface. Excessive amniotic fluid may result from abnormal amniotic membrane function, impaired fetal swallowing of amniotic fluid, or increased fetal excretion. Polyhydramnios is frequently associated with fetal structural anomalies. In acute cases, it typically occurs around the 28th week of gestation. Rapid uterine distension due to acute polyhydramnios poses a serious threat to fetal survival; therefore, pregnant women must exercise particular caution.

2. Chronic polyhydramnios

Chronic polyhydramnios generally requires no excessive concern. Mild cases often resolve with adequate rest and appropriate lifestyle adjustments. Many clinicians recommend a low-salt diet during this period. Nevertheless, pregnant women should undergo regular monitoring and close observation of amniotic fluid volume. If rapid accumulation of amniotic fluid or worsening symptoms occur, amniocentesis may be performed to drain excess fluid and reduce uterine size. Importantly, drainage must proceed gradually to avoid premature placental abruption.

How is polyhydramnios managed?

1. For severe symptoms intolerable to the mother (with gestational age < 37 weeks), therapeutic amniocentesis may be performed. The volume drained per session should not exceed 1500 mL, aiming to alleviate maternal symptoms. Excessive drainage may precipitate preterm labor.

2. Indomethacin therapy: Indomethacin inhibits fetal renal blood flow and reduces fetal urine production, thereby decreasing amniotic fluid volume. Weekly B-mode ultrasonography is required to monitor amniotic fluid volume during treatment. In late pregnancy, fetal urine constitutes the primary source of amniotic fluid.

3. At or near 37 weeks’ gestation, if fetal maturity is confirmed, artificial rupture of membranes may be performed to induce delivery.

4. For mild symptoms, continuation of pregnancy is possible with emphasis on rest, a low-salt diet, and judicious use of sedatives, while closely monitoring changes in amniotic fluid volume.

The above outlines the potential effects of polyhydramnios on the fetus and summarizes key management strategies. We hope this information proves helpful.