What Is the Function of the Amniotic Sac?

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John Hopkins Medicine states that the amniotic sac, the fluid-filled sac that holds the fetus in the uterus, functions to protect the unborn baby and help regulate the baby's temperature. The amniotic fluid inside the sac cushions the fetus and protects the fetus from damage. The amniotic sac also hold the amnion, a membrane that separates the placenta from the amniotic fluid.

Vanderbilt University Medical Center explains that in addition to protecting the fetus from physical dangers, the amniotic sac keeps outside contaminants, such as germs, from reaching the fetus. If the amniotic sac breaks before the fetus is ready to be born, complications are likely to develop. The fetus becomes vulnerable to infection from germs. The umbilical cord, which supplies the fetus with oxygen and nutrients, may become compressed without the cushioning of the amniotic fluid. The placenta may separate from the uterine wall if the amnion is damaged, which can causing internal bleeding. Premature birth is likely.

Vanderbilt University Medical Center lists the primary symptom of a leaking amniotic sac, also known as premature rupture of the membranes, to be a leaking or gushing water-like discharge from the vagina. The fluid sometimes has a yellow tinge. Other possible symptoms include vaginal bleeding and pain in the lower abdomen or lower back.