The role of amniotic fluid

Inside a pregnant woman’s uterus is an amniotic sac, which contains amniotic fluid and the growing fetus.

The amniotic fluid is important for several reasons -- it helps keep the baby warm, and because his body parts are growing so fast, the fluid provides lubrication that keeps them from growing together. In some cases, fingers and toes can become webbed as a result of not enough amniotic fluid circulating in the uterus.

The amniotic fluid also lets the baby move easily so he can exercise his muscles and strengthen his bones before he’s born.

In addition, it acts like a liquid shock absorber for the baby by distributing any force that may push on the mother’s uterus. Even sex won’t hurt the baby.

Amniotic fluid is 98% water and 2% salts and cells from the baby. Until the fetal kidneys started working during month four, amniotic fluid is made by the mother’s body. But after month four, the little guy started to make his contribution to the amniotic fluid by urinating in it.

You heard right. It may not sound appealing to us, but the urine in the amniotic sac is completely harmless to the baby.

The baby swallows amniotic fluid, which then passes through his digestive system, into his kidneys, and back out again to the amniotic sac as urine. In this way, he can practice using his digestive and urinary systems before he’s even born. In fact, doctors can tell by the amount of amniotic fluid whether the baby has difficulty with his swallowing reflex.

By the time he’s born, he will consume up to 13 ounces of amniotic fluid a day.

Review Date: 10/15/2024

Reviewed By: John D. Jacobson, MD, Professor Emeritus, 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.

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06/01/2025

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