Polyhydramnios is a common complication of pregnancy. It means there's an excessive amount of amniotic fluid surrounding the unborn baby (foetus).
An abnormal amount of fluid (whether increased or reduced) might be suspected by your healthcare professional after 30 weeks of pregnancy, during one of your antenatal appointments, and should be monitored and investigated.
The cause of polyhydramnios is often not known, but sometimes indicates a problem with the development of the baby (see What are the causes?, below). However, most women with polyhydramnios give birth to healthy babies.
If you're pregnant and notice that your belly is getting large very quickly (acute polyhydramnios), contact your doctor or midwife. It is rare for it to happen this suddenly, but it can indicate an abnormality with the foetus (unborn baby) and increase your risk of giving birth prematurely.
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In most women with polyhydramnios, the excess fluid builds up slowly. After 30 weeks of pregnancy, this excess fluid should be noticeable and picked up by your doctor, midwife or obstetrician during one of your antenatal appointments.
In rare cases, when polyhydramnios develops very quickly, the excess fluid may be apparent earlier in pregnancy, or might be noted at the time of the detailed scan at 18-22 weeks.
If increased amniotic fluid is suspected, you may be referred for an [ultrasound scan] so the depth of the amniotic fluid surrounding the foetus can be measured.
Often, no cause can be found for polyhydramnios. However, it can be associated with any of the following:
Having polyhydramnios means there's a slightly higher risk of your unborn baby having a birth defect, especially if the fluid build-up is severe. You should discuss any other problems the extra fluid could be linked to with your healthcare professionals.
However, don't panic – the vast majority of women with polyhydramnios give birth to healthy babies.
Your labour may be affected in the following ways:
Most women with polyhydramnios will need an ultrasound investigation and a glucose tolerance test, to try and identify a cause and check for gestational diabetes.
If your condition is not severe, this can be done in the doctor's surgery and you may not need to be admitted to hospital. Read more about [ultrasound scans in pregnancy].
If the ultrasound scan appears to show a problem with the foetus, doctors might discuss whether you wish to have an amniocentesis (where a sample of fluid is drawn out using a needle), to test for chromosomal or genetic problems in the foetus.
Your doctors and midwives may recommend that you give birth to the baby in hospital, and may recommend close monitoring of the baby's heart rate in labour.
If your baby appears normal after birth, your doctor might suggest passing a tube down your baby's throat to check them for internal problems, such as a problem with the development of their gullet (oesophageal atresia).
Read general information about [your baby after the birth].
Important: Our website provides useful information but is not a substitute for medical advice. You should always seek the advice of your doctor when making decisions about your health.