Amniotic fluid is a clear, slightly yellowish liquid that surrounds the unborn baby (fetus) during pregnancy. It is contained in the amniotic sac.
While in the womb, the baby floats in the amniotic fluid. The amount of amniotic fluid is greatest at about 34 weeks (gestation) into the pregnancy, when it averages 800 mL. About 600 mL of amniotic fluid surrounds the baby at full term (40 weeks gestation).
The amniotic fluid constantly moves (circulates) as the baby swallows and "inhales" the fluid, and then releases it.
The amniotic fluid helps:
The developing baby to move in the womb, which allows for proper bone growth
The lungs to develop properly
Keep a constant temperature around the baby, protecting from heat loss
Protect the baby from outside injury by cushioning sudden blows or movements
Too much amniotic fluid is called polyhydramnios. This condition can occur with multiple pregnancies (twins or triplets), congenital anomalies (problems that exist when the baby is born), or gestational diabetes.
Too little amniotic fluid is known as oligohydramnios. This condition may occur with late pregnancies, ruptured membranes, placental dysfunction, or fetal abnormalities.
Abnormal amounts of amniotic fluid may cause the health care provider to watch the pregnancy more carefully. Removing a sample of the fluid through amniocentesis can provide information about the sex, health, and development of the fetus.
Cunningham FG, Leveno KJ, Bloom SL, et al. Embryogenesis and fetal morphological development. In: Cunningham FG, Leveno KL, Bloom SL, et al, eds. Williams Obstetrics. 24th ed. New York, NY: McGraw-Hill; 2040:chap 7.
Gilbert WM. Amniotic fluid disorders. In: Gabbe SG, Niebyl JR, Simpson JL, et al, eds. Obstetrics: Normal and Problem Pregnancies. 6th ed. Philadelphia, PA: Elsevier Saunders; 2012:chap 33.
Ross MG, Ervin MG, Novak D. Placental and fetal physiology. In: Gabbe SG, Niebyl JR, Simpson JL, at al, eds. Obstetrics: Normal and Problem Pregnancies. 6th ed. Philadelphia, PA: Elsevier Saunders; 2012:chap 2.
Irina Burd, MD, PhD, Assistant Professor of Gynecology and Obstetrics at Johns Hopkins University School of Medicine, Baltimore, MD. Review provided by VeriMed Healthcare Network. Also reviewed by David Zieve, MD, MHA, Isla Ogilvie, PhD, and the A.D.A.M. Editorial team.