Polyhydramnios

During pregnancy, the baby is surrounded by amniotic fluid inside the mother’s uterus. Amniotic fluid plays an important role—in protecting the baby, by cushioning against blows to the mother’s abdomen. It also allows the baby to move more freely, which promotes muscular and skeletal development. Additionally, the baby swallows amniotic fluid during pregnancy, which helps the baby’s gastrointestinal tract to develop.

In approximately 1% of pregnancies there is an excess of amniotic fluid, known as polyhydramnios. Clinical signs and symptoms of polyhydramnios include swelling, abdominal size that increases out of proportion for weight gain and gestational age, decreased maternal urine production, shortness of breath and chest heaviness. Your physician or midwife may suspect polyhydramnios after an examination of your abdomen.

Mothers who develop polyhydramnios earlier in pregnancy and those with greater amounts of excess amniotic fluid are at increased risk for complications. These risks include premature birth, premature rupture of membranes (when the “water” breaks early), excess fetal growth, placental abruption, umbilical cord prolapse (when the umbilical cord drops into the vagina before the baby), C-section delivery, stillbirth, and heavy bleeding due to lack of uterine muscle tone after delivery.

There are many causes of polyhydramnios, including conditions where the baby’s ability to swallow or kidney functions are impaired. Swallowing and processing fluid through the kidneys regulates the amount of amniotic fluid, so when these processes are not functioning properly, excess fluid may accumulate. Polyhydramnios can also be caused by maternal diabetes, reduced red blood cells in the baby (fetal anemia), blood incompatibilities between mother and baby, and twin-twin transfusion—a complication that can occur in identical twin pregnancies when one twin receives too much blood and the other too little. However, the cause of polyhydramnios is often unknown.

Polyhydramnios can be diagnosed and assessed during an ultrasound by measuring the amniotic fluid index (AFI). AFI is calculated by dividing the uterus into 4 quadrants and adding up the depth (in centimeters) of the 4 different quadrants (pockets) of amniotic fluid. The normal amount of fluid is about a quart. In polyhydramnios, the amount can be up to a half-gallon. While the normal range for AFI depends on the gestational age of the baby, physicians generally agree than an AFI of more than 25 cm is polyhydramnios. In some cases, a physician may consider lower AFIs as polyhydramnios.

Most cases of polyhydramnios are mild, with an AFI of less than 30. Expectant mothers with mild polyhydramnios often do not require treatment, and the condition may resolve on its own. In other cases, treatment of the underlying condition—such as diabetes—may help resolve polyhydramnios.

Mothers with severe polyhydramnios may need treatment, which can include medication and/or draining the excess amniotic fluid through amniocentesis. Since the baby continues to make amniotic fluid throughout the pregnancy, it may be necessary to have the excess fluid drained several times before birth.

If you have been diagnosed with polyhydramnios, or are concerned that you may have polyhydramnios, it is important to speak to your health care provider regarding your specific risks and treatment options.