Causes of polyhydramnios

Possible causes include diabetes arising during pregnancy, a multiple pregnancy, certain infections, or a fetal condition that affects swallowing or fluid balance. In pregnancies with shared placental circulation, an imbalance of blood flow between babies can also increase fluid around one baby.

Later in pregnancy, the baby contributes to amniotic fluid by passing urine and removes fluid by swallowing it. Polyhydramnios can develop when urine production rises, swallowing is reduced, or fluid circulation is altered. The finding may be mild and discovered during a routine scan, or the fluid can increase more quickly and stretch the uterus.

A larger uterus may contribute to abdominal tightness, indigestion, breathlessness or swelling, although these symptoms also occur in pregnancies without excess fluid. The scan measurement and the wider pregnancy assessment, rather than symptoms alone, establish whether polyhydramnios is present.

Your maternity team may repeat ultrasound measurements, review the baby’s anatomy and growth, and check for diabetes during pregnancy. Blood tests may be considered when symptoms, medical history or scan findings suggest infection or another underlying condition. Follow the monitoring schedule even when you feel well, because fluid levels and the baby’s position can change.

Management depends on the amount of fluid, symptoms, gestational stage and any identified cause. Care may focus on treating an underlying condition and observing the pregnancy more closely. When severe fluid pressure causes significant symptoms, a specialist may discuss removing some fluid with a needle, together with the procedure’s benefits and risks.

Contact your maternity unit urgently if your abdomen becomes larger suddenly, you develop new or worsening abdominal pain, your waters break, contractions begin, breathing becomes difficult, or your baby’s usual movements reduce or change. If fluid comes from the vagina, use a pad rather than a tampon and note its colour while arranging immediate assessment.

Ask how much extra fluid was seen, whether the finding has changed, and whether the baby’s anatomy and growth appear as expected. Discuss which checks for diabetes or infection are appropriate, how often monitoring is planned, whom to call if symptoms change, and whether the finding affects recommendations for labour or place of birth.