Causes of polyhydramnios in the third trimester

Possible contributors include diabetes during pregnancy, a multiple pregnancy, fetal anaemia, infection, or a condition that affects how the baby swallows or processes fluid. Finding extra fluid does not by itself identify the cause, and many cases remain unexplained.

Amniotic fluid is continually produced and removed. Later in pregnancy, much of it comes from the baby's urine and is recycled when the baby swallows. Polyhydramnios develops when production exceeds removal.

An ultrasound can estimate fluid volume, review growth, look at the baby's anatomy and check whether there is more than one baby. Your maternity team may also review glucose testing and consider other tests according to the scan and your health history.

Keep the follow-up appointments offered by your maternity team. Monitoring may include repeat ultrasound assessment, checks of fetal movement and wellbeing, and discussion of where and how to give birth if the fluid remains high.

Notice your baby's usual movement pattern rather than relying on a fixed daily count. Contact maternity triage promptly if movements become reduced or clearly different. Do not try to reduce fluid by restricting drinks unless a clinician has given you a separate medical reason to do so.

Call your maternity unit urgently for a sudden gush or ongoing trickle of fluid, vaginal bleeding, regular painful tightenings, marked breathlessness, severe abdominal discomfort, or reduced fetal movement. If the waters break, avoid inserting anything into the vagina and follow the unit's instructions, because excess fluid can alter how the baby or umbilical cord sits.

Call emergency services for severe breathing difficulty, collapse, heavy bleeding, or if you can feel or see the umbilical cord or any part of the baby at the vagina.

Ask how much extra fluid was seen, whether growth and anatomy appeared reassuring, whether glucose or infection testing is appropriate, and when another scan is planned. You can also ask how the finding affects monitoring, labour planning and what to do if your waters break at home.