What is polyhydramnios?

Polyhydramnios: Too Much Amniotic Fluid
When a woman has polyhydramnios, the level of amniotic fluid surrounding the baby is too high.

What You Need to Know About Polyhydramnios
Polyhydramnios (too much amniotic fluid) occurs in about 2 out of 100 of pregnancies. Most cases are mild and result from a slow buildup of excess fluid in the second half of pregnancy. But in a few cases, fluid builds up as early as the 16th week of pregnancy. This usually leads to very early delivery.

Polyhydramnios is diagnosed with ultrasound. Medical experts do not fully understand what causes this condition. In 2 out 3 cases, the cause is not known. Here are two of the best-known causes:

Birth defects in the baby that affect the ability to swallow. Normally, when the fetus swallows, the level of amniotic fluid goes down a bit. This helps to balance out the increase in fluid caused by fetal urination.
Heart defects in the baby.

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