The amniotic fluid is part of the baby’s life support system. It protects your baby and aids in the development of muscles, limbs, lungs and the digestive system. Amniotic fluid is produced soon after the amniotic sac forms, about 12 days after conception. It is first made up of water that is provided by the mother. After about 20 weeks into the pregnancy, it is primarily made up of fetal urine. As the baby grows, he or she will move and tumble in the womb with the help of the amniotic fluid. In the second trimester the baby will begin to breathe and swallow the amniotic fluid. Amniotic fluid levels increase regularly until about 32-33 weeks gestation, and then they level off. In some cases the amniotic fluid may measure too low or too high. Normal fluid levels may vary, but are usually considered an AFI of 5-25 centimeters or a fluid level of about 800-1000 mL. If the measurement of amniotic fluid is too low it is called oligohydramnios. If the measurement of amniotic fluid is too high it is called polyhydramnios.
What is Polyhydramnios?
Polyhydramnios is the condition of having too much amniotic fluid. Doctors can measure the amount of fluid through a few different methods, most commonly through amniotic fluid index (AFI) evaluation or deep pocket measurements. If an AFI shows a fluid level of more than 25 centimeters (or above the 95th percentile), a single deep pocket measurement of <8, or a fluid level of 2000mL or more, then a diagnosis of polyhydramnios would be made. About 1-2% of pregnant women have too much amniotic fluid. Most of these cases are mild, with only slightly elevated levels.
What causes levels of amniotic fluid to be elevated?
Congenital defects – The higher the fluid level, the increased chance of a congenital defect. These birth defects hinder swallowing, which can prohibit ingestion of the amniotic fluid, resulting in build up of fluid. Other birth defects could also include intestinal tract blockage or neurological abnormalities.
Rh Factor – As screening for the Rh factor has increased, this is no longer a common cause of elevated fluid levels.
Maternal Diabetes – Experts have found some correlation between diabetes and too much amniotic fluid.
Twin-to-twin transfusion syndrome – This is a complication that can affect identical twin pregnancies. This syndrome is when one baby gets too much blood flow and the other too little due to connections between blood vessels in their shared placenta.
Unknown Reasons – According to the Center for Maternal Fetal Medicine, about 65% of cases of polyhydramnios are due to unknown causes.
What are the risks of having too much amniotic fluid?
Most cases of polyhydramnios are mild and result in few, if any, complications. Those with higher levels of fluid could experience one or more of the following risks:
- Premature rupture of the membranes (PROM)
- Placenal abruption
- Preterm labor and delivery (approximately 26%)
- Growth restriction (IUGR) resulting in skeletal malformations
- Stillbirth occurs in about 4 in 1000 pregnancies that suffer from polyhydramnios vs. about 2 in1000 pregnancies with normal fluid levels.
- Cesarean delivery
- Postpartum hemorrhage
What are the treatments for elevated amniotic fluid levels?
Many cases of polyhydramnios are easily treated and do not result in complications if the pregnancy is monitored closely. Monitoring would include frequent sonograms measuring growth, biophysical profile and fetal assessment. Other treatments could include:
- Medication that can reduce fluid production and are as much as 90% effective. This treatment is not used after 32 weeks gestation because of possible complications.
- Amnioreduction is a procedure that can be used to drain excess fluids. This is done through amniocentesis, which may carry certain risks. There is, however, the chance that fluid could build back up even after draining.
- Delivery of the baby
1 Morales WJ, Talley T: Premature rupture of membranes at less than 25 weeks: a management dilemma. Am J Obstet Gynecol 1993 Feb; 168(2): 503-7[Medline].
1Chamberlain PF, Manning FA, Morrison I, et al: Ultrasound evaluation of amniotic fluid volume. II. The relationship of increased amniotic fluid volume to perinatal outcome. Am J Obstet Gynecol 1984 Oct 1; 150(3): 250-4[Medline].