Is Too Much Amniotic Fluid During the Third Trimester Cause for Concern?

Polyhydramnios (high amniotic fluid) is a rare condition—but is it a cause for worry, especially during the third trimester? Here's what you need to know.

fetal development
Photo: SebastianKaulitzki/shutterstock.com

Amniotic fluid plays a crucial role in the development of your unborn baby. It cushions and protects the fetus, from external pressures, blows, and harm. It regulates body temprature, helping to maintain the status quo, and amniotic fluid helps with the development of your unborn baby's lungs, muscles, bones, and digestive system. In most cases, it poses no threat or harm. But in rare cases, amniotic fluid can be problematic, particularly when one has too much or too little.

Here's everything we know about polyhydramnios, a medical condition which occurs when one has an excess amount of amniotic fluid.

What is Polyhydramnios?

Polyhydramnios only occurs in about 1% of pregnancies. To be diagnosed with this condition, one must have more than 25 centimeters of amniotic fluid. Normal amniotic fluid levels are between five and 24 centimeters, or about 800 to 1000 mL. The range, however, depends on how far along you are, as the fluid levels will increase as your pregnancy progresses

How Is Polyhdramnios Diagnosed?

If your doctor suspects polyhydramnios, testing will be done. This is to determine if you have the condition and, if so, if the excess amount of amniotic fluid is cause for concern.

The tests themselves are painless, noninvasive, and safe—for both you and baby. Your doctor may use the Amniotic Fluid Index (AFI) to measure the amount of fluid in four different areas of the uterus, or they may chose to measure the deepest pocket of fluid within the uterus. With this test, polyhdramnios is diagnosed when measurements exceed 8cm. Usually, however, the condition doesn't cause much trouble, especially during the latter part of pregnancy. Most pregnant people with polyhydramnios will not have any significant problems.

What Are the Causes of Polyhydramnios?

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

  • Birth defects, specifically those involving your unborn baby's ability to swallow and/or affecting their kidney function
  • Diabetes
  • Rh Incompatibility, or a mismatch between the mom's blood and the unborn baby's blood
  • Twin-to-twin transfusion syndrome (TTTS), which occurs when one identical twin gets too much blood flow and the other gets too little
  • Problems with the unborn baby's heart rate
  • Fetal infection

What Are the Effects of High Amniotic Fluid?

While 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—the risk is low. As previously mentioned, most pregnant people will carry their fetus to term (and go on to deliver a healthy baby). That said, polyhydramnios increases the risk of premature rupture of membranes and/or preterm labor. What's more, some unborn 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 baby is born, and increased risk for postpartum hemorrhage.

While these all sound scary, and they're all possible when a pregnant person has polyhydramnios, they're also very unlikely, especially if your unborn 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.

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