Too Much Amniotic Fluid During Your Third Trimester

Cause for worry, or not so much? Polyhydramnios (high amniotic fluid) is a rare condition, but here's what you need to know about it.

fetal development
Photo: SebastianKaulitzki/

The amniotic fluid that your baby swims in for 9 months plays a crucial role in her health. Your baby needs just the right amount to protect her and help her grow. Normal amniotic fluid levels in the later stages of pregnancy are between 5 and 25 centimeters, or about 800-1000 mL. If the measurement is over 25, it's called polyhydramnios – a condition which leads to increased risks for mom and Baby.

What is Polyhydramnios?

Polyhydramnios only occurs in about 1% of pregnancies. Mild cases during the latter part of pregnancy usually don't cause much trouble, and the condition is commonly seen with chubby babies. Severe cases of polyhydramnios are rare and sometimes seen with babies who have blockage along the gastrointestinal tract. About 50 - 65% of the time, nobody knows what causes a woman to develop polyhydramnios. The rest of the time, they can pinpoint it to one of the following conditions.

Causes of Polyhydramnios

The following factors may lead to an increased risk of polyhydramnios, which is characterized by too much amniotic fluid:

  • Birth defects involving Baby's ability to swallow or kidney function: It's your baby's ability to swallow and process fluid through the kidneys that regulates the amount of fluid in the uterus.
  • Diabetes: Some moms with diabetes might have increased levels of fluid.
  • Rh Incompatibility: A mismatch between mom's blood and Baby's blood.
  • Twin-to-twin transfusion syndrome (TTTS): When one identical twin gets too much blood flow and the other gets too little.
  • Problems with the baby's heart rate: These likely show up on ultrasound or monitoring
  • An infection in the baby

Effects of High Amniotic Fluid

As a worst case scenario, too much amniotic fluid is associated with an increased risk of stillbirth. In pregnancies involving normal amniotic fluid levels, 2 out of 1,000 babies are stillborn. With polyhydramnios, it's 4 out of 1,000 – but that still means that 996 of those 1000 are born alive.

Polyhydramnios increases the risk of premature rupture of membranes and/or preterm labor. What’s more, some babies with high amniotic fluid levels can wiggle their way into a weird birthing position. Instead of assuming the normal late-pregnancy, head down, ready-to-be-born position, polyhydramnios increases risks for breech or transverse positions, which increase chances for C-section.

Another possible complication involves labor itself: the umbilical cord could get pinched or pushed out before the baby, which can be very dangerous. Finally, too much amniotic fluid could lead to placental abruption, which means the placenta could separate before the baby is born, and increased risk for postpartum hemorrhage.

While these all sound scary, and they're all possible when mom has polyhydramnios, they're also very unlikely. As long as your baby is close to term, your amniotic fluid is still near normal range, and you're being taken care of by a trained healthcare team that knows what to do, high amniotic fluid levels shouldn’t be a problem. Your doctor will monitor your baby's well-being with nonstress tests and biophysical profiles. If the fluid level drops too much, your doctor may recommend an early delivery.

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