Amniotic fluid—Fluid inside the membrane that forms a sac around the embryo and later the fetus. The fetus and the placenta produce the amniotic fluid. This buoyant fluid helps the fetus grow uniformly, helps the bones and muscles develop, and allows the baby to move within the uterus. Babies breathe this fluid in and out of their lungs in the womb helping the lungs to grow as well. It also keeps the amnion (membrane) from sticking to the fetus.
Having too little or too much amniotic fluid can signal a problem with the fetus or the mother. A mild decrease in amniotic fluid is common late in pregnancy. Too much amniotic fluid may cause the uterus to enlarge, which may result in premature labor. Excess fluid occurs in maternal diabetes, twins and some other conditions. Fetal problems that may also result in excess fluid are esophageal astresia (blockage of the esophagus that prevents effective swallowing) which prevents the amniotic fluid from passing to the stomach and intestines for absorption.