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. Approximately 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 relatively constant temperature around the baby, protecting from heat loss
Protect the baby from outside injury by cushioning sudden blows or movements
An excessive amount of amniotic fluid is called polyhydramnios. This condition can occur with multiple pregnancy (twins or triplets), congenital anomalies (problems that exist when the baby is born), or gestational diabetes.
An abnormally small amount of 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. Removal of a sample of the fluid, through amniocentesis, can provide information about the sex, health, and development of the fetus.
Ross MG, Ervin MG, Novak D. Fetal physiology. In: Gabbe SG, Niebyl JR, Simpson JL, eds. Obstetrics: Normal and Problem Pregnancies. 5th ed. Philadelphia, Pa: Elsevier Churchill Livingstone; 2007:chap 2.
Gilbert WM. Amniotic fluid disorders. In: Gabbe SG, Niebyl JR, Simpson JL, eds. Obstetrics: Normal and Problem Pregnancies. 5th ed. Philadelphia, Pa: Elsevier Churchill Livingstone; 2007:chap 31.
Cunningham FG, Leveno KJ, Bloom SL, et al. Fetal growth and development. In: Cunningham FG, Leveno KL, Bloom SL, et al, eds. Williams Obstetrics. 23rd ed. New York, NY: McGraw-Hill; 2010:chap 4.
Linda J. Vorvick, MD, Medical Director, MEDEX Northwest Division of Physician Assistant Studies, University of Washington, School of Medicine; Susan Storck, MD, FACOG, Chief, Eastside Department of Obstetrics and Gynecology, Group Health Cooperative of Puget Sound, Bellevue, Washington; Clinical Teaching Faculty, Department of Obstetrics and Gynecology, University of Washington School of Medicine. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.