Polyhydramnios: causes, symptoms and what it means for pregnancy

The NHS says the cause of polyhydramnios is often unknown. The possible causes it lists are gestational diabetes, being pregnant with more than 1 baby, an infection during pregnancy, a problem with your baby swallowing, and your baby having a genetic condition.

Leeds Teaching Hospitals gives more detail in its Fetal Medicine Unit leaflet. In most pregnancies with extra amniotic fluid no cause is found and babies are healthy when they are born. Less commonly, the baby may wee more than average if you have developed gestational diabetes; in a monochorionic twin pregnancy (twins sharing a placenta) extra fluid may be a sign of twin-to-twin transfusion syndrome; something may be obstructing the passage of fluid through the baby's gut; or, rarely, a brain or muscle abnormality may cause a problem with swallowing.

Amniotic fluid cushions the baby and protects it from trauma, and helps with the development of the baby's lungs, muscles and joints. Leeds Teaching Hospitals explains that polyhydramnios is diagnosed when the amount of fluid is above the expected normal range, which changes depending on how many weeks pregnant you are, and that it can only be diagnosed following an ultrasound scan.

The NHS says polyhydramnios does not usually cause symptoms. If there are symptoms they might include indigestion and heartburn, constipation, breathlessness, swollen feet and legs and urinary tract infections. These could also be usual symptoms in pregnancy.

If the fluid increases quickly it can cause tummy pain and make your tummy get bigger suddenly, which the NHS says is more common if you are expecting more than 1 baby.

You may only find out at a routine appointment. The NHS says the sonographer doing your ultrasound scan may see the extra fluid, or your midwife may notice that you are larger than expected for your due date. It may also be harder to hear the baby's heartbeat because of the extra fluid.

If you have symptoms, such as your tummy getting bigger suddenly, you may be referred for an ultrasound scan, and a sonographer will measure the amount of amniotic fluid around the baby. Leeds Teaching Hospitals says the local hospital may refer you to a fetal medicine unit if the volume is large (in its region, 30 cm or more), where doctors assess the baby in detail and plan monitoring.

The NHS says polyhydramnios usually does not need any treatment. You may have extra check-ups for the rest of your pregnancy and during labour and birth. If it is caused by a condition such as gestational diabetes, you will be treated for that condition.

If you have severe polyhydramnios, some of the amniotic fluid may be drained from the womb using a thin needle. You may need this more than once and you will be monitored afterwards to check your fluid levels.

Leeds Teaching Hospitals says that if the extra fluid is an isolated finding and your baby appears healthy on the scan, it is not likely to have a negative impact on your baby. In some situations your baby may not settle head first, and the bigger womb can make waters breaking before the due date more likely. If the baby's head is not engaged at that point there is a risk of the umbilical cord coming first, which is an emergency and may need delivery by caesarean section.

The NHS says complications are rare. In more severe cases they can include waters breaking early (call your midwife straight away if this happens), placental abruption, umbilical cord prolapse, premature birth and low birth weight. If you have moderate or severe polyhydramnios you may be advised to give birth in hospital, where you can be monitored closely and treatment is available quickly, and you may have a higher chance of needing a caesarean. Speak to your midwife if you have concerns about your labour and birth plans.

The NHS says to ask for an urgent GP appointment, contact your midwife or get help from NHS 111 if your tummy gets bigger suddenly or you have tummy pain. If your waters break, call your midwife straight away. Contact your maternity unit or call 999 if you have heavy bleeding or severe constant pain, which can be signs of placental abruption.

The sources read for this page do not describe a diet or home remedy that reduces amniotic fluid. If gestational diabetes is found as the cause, your team will treat it, which may include diet advice specific to that condition. Do not restrict fluids without advice from your midwife or obstetrician.

On the NHS, polyhydramnios is picked up through routine antenatal scans and midwife checks, with obstetric review and, where needed, referral to a fetal medicine unit. Private antenatal scans can also detect it, but the follow-up scans, glucose testing, delivery planning and any amniotic fluid drainage are provided through NHS maternity and fetal medicine services. If you are told you have extra fluid on a private scan, tell your midwife so it can be followed up in your NHS maternity record.