Polyhydramnios (too much amniotic fluid)


Polyhydramnios (too much amniotic fluid)


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.

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.

This page covers:

How is polyhydramnios diagnosed?

What are the causes?

What associated risks should I be aware of?

How is it investigated and managed?


How is polyhydramnios diagnosed?

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 GP, midwife or obstetrician during one of yourantenatal 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 anultrasound scan so the depth of the amniotic fluid surrounding the foetus can be measured.

What are the causes?

Often, no cause can be found for polyhydramnios. However, it can be associated with any of the following:

The mother carrying twins

The mother having diabetes, including gestational diabetes (pregnancy-related diabetes). Sometimes, if diabetes is the cause, the baby will be larger than expected for its stage of development.

A blockage in part of the baby's gut (a condition called gut atresia), which prevents them absorbing the usual amount of amniotic fluid. A gut atresia would often require an operation after the baby's birth

The mother having rhesus disease, where antibodies in the mother's blood cross the placenta, sometimes causing anaemia in the foetus.  

A growth of blood vessels on the placenta, called a chorioangioma.

A build up of fluid in specific areas of the baby's body, such as the abdomen and chest cavity, called hydrops fetalis.

A genetic problem with the foetus.

What associated risks should I be aware of?

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:

you may go into premature labour due to the additional pressure stretching the womb

your baby may be in the wrong position and you may need aCaesarean section

if your baby is in the wrong position, the umbilical cord may slip down into the birth canal when the membranes rupture 

you may have an increased risk of bleeding after delivery


How is it investigated and managed?

Most women with polyhydramnios will need an ultrasound investigation and a glucose tolerance test, to try and identify a cause and check forgestational diabetes. 

If your condition is not severe, this can be done in the GP's surgery and you may not need to be admitted to hospital.

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. 

During and after labour

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).


Amniotic fluid: what does it do? 

During pregnancy, the unborn baby (foetus) floats inside a fluid-filled sac in the womb.

Amniotic fluid has several important roles:

it protects the foetus from outside injury by cushioning sudden blows and movements

it helps the foetus to move in the womb, allowing for proper bone growth

it helps the foetus' lungs develop properly

it keeps the temperature relatively constant around the foetus

The fluid constantly moves around as the foetus swallows it and releases it through urine.  

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Polyhydramnios too much amniotic fluid