Amniotic Fluid Imbalances

Amniotic fluid is a changing measure of the fetal–placental system, not simply a cushion around the fetus. In later pregnancy, fetal urine is its major source; fetal swallowing and absorption remove fluid. The ultrasound pocket therefore reflects the balance between fetal urine production, swallowing, membrane integrity, and placental function. Oligohydramnios means too little fluid. A leak from ruptured membranes, reduced placental perfusion, reduced fetal urine production, or medication exposure can lower the volume. With less cushioning, the umbilical cord is more easily compressed, producing variable fetal heart rate decelerations. When oligohydramnios begins early and is severe, restricted fetal movement and prolonged compression can impair lung development and cause musculoskeletal deformities. Later-onset oligohydramnios is more often a marker of placental insufficiency and may occur with fetal growth restriction. Polyhydramnios means too much fluid. It may result from increased fetal urine production, as can occur with maternal diabetes, or reduced fetal swallowing from gastrointestinal, neurological, or structural problems. Uterine overdistension can cause maternal dyspnoea, preterm contractions, malpresentation, dysfunctional labour, postpartum uterine atony, and haemorrhage. Once the membranes rupture, the excess fluid also...