Polyhydramnios

Some conditions of the unborn baby or pregnancy can give rise to excess amniotic fluid, says Dr Howard Lee

What is amniotic fluid?

Amniotic fluid is usually sterile, and contained in the sac that surrounds a baby throughout pregnancy.

It helps to protect and cushion, and also plays an important part in developing many of the baby's vital internal organs - like the lungs, kidneys and gut.

The normal amount may vary, but there's usually a slow increase until about 36 weeks of pregnancy - then a slow decrease. Most women carry about 500 ml of amniotic fluid.

The fluid is produced by the inner lining of the sac (amnion) as well from the baby's lungs and kidneys - it is continually taken up by the baby's swallowing, and is also sent across the afterbirth (placenta) into the mother's circulation.

The most common problems with amniotic fluid - which occur in about seven out of every 100 pregnancies - usually take the form of either too much fluid (hydramnios or polyhydramnios) or too little fluid (oligohydramnios).

Both conditions are associated with abnormalities in the baby's development or some other pregnancy complication. Any abnormal difference in the amount of amniotic fluid present may be the cause or the result of a problem within a pregnancy.