Amniotic fluid
Amniotic fluid is a clear, slightly yellowish liquid that surrounds the unborn baby (fetus) during pregnancy. It is contained in the amniotic sac.
Amniocentesis is used to determine the health of an unborn baby. Amniotic fluid contains cells that are normally shed from the fetus. Samples of these cells are obtained by withdrawing some amniotic fluid. The chromosome analysis of these cells can be performed to determine abnormalities. In addition, the cells may be cultured and analyzed for enzymes, or for other materials that may indicate genetically transmitted diseases. Other studies can be done directly on the amniotic fluid including measurement of alpha-fetoprotein.
Amniotic fluid not only protects the fetus from injury and temperature changes, it also is circulated by the fetus every 3 hours.
Polyhydramnios may occur when a fetus cannot swallow a normal amount of amniotic fluid due to a gastrointestinal, neurological, or other problem.
Amniotic fluid surrounds the growing fetus in the womb and protects the fetus from injury and temperature changes. It also allows for freedom of fetal movement and permits musculoskeletal development. The amniotic fluid can be withdrawn in a procedure called amniocentesis to check for chromosomal defects or other abnormalities.
Information
While in the womb, the baby floats in the amniotic fluid. The amount of amniotic fluid is greatest at about 34 weeks into the pregnancy (34 weeks gestation), 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
- Prevent pressure on the umbilical cord
- 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.
References
Burton GJ, Sibley CP, Jauniaux ERM. Placental anatomy and physiology. In: Landon MB, Galan HL, Jauniaux ERM, et al, eds. Gabbe's Obstetrics: Normal and Problem Pregnancies. 8th ed. Philadelphia, PA: Elsevier; 2021:chap 1.
Gilbert WM. Amniotic fluid disorders. In: Landon MB, Galan HL, Jauniaux ERM, et al, eds. Gabbe's Obstetrics: Normal and Problem Pregnancies. 8th ed. Philadelphia, PA: Elsevier; 2021:chap 28.
Ross MG, Beall MH. Amniotic fluid dynamics. In: Lockwood CJ, Copel JA, Dugoff L, et al, eds. Creasy and Resnik's Maternal-Fetal Medicine: Principles and Practice. 9th ed. Philadelphia, PA: Elsevier; 2023:chap 4.
Version Info
Last reviewed on: 11/10/2022
Reviewed by: John D. Jacobson, MD, Department of Obstetrics and Gynecology, Loma Linda University School of Medicine, Loma Linda, CA. Also reviewed by David C. Dugdale, MD, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.
