What is the amniotic sac?

Thin membrane: The amnionic sac is a thin membrane holding the amnionic fluid around the baby. If you experience clear leakage of fluid during pregnancy, your amnionic sac may have broken and it is important to see your obgyn for an exam and possibly an ultrasound. If not recognized, labor or infection may begin.

Amniotic sac: The amniotic sac (also bag of waters) is the sac in which the fetus develops in amniotes. It is a tough but thin transparent pair of membranes, which hold a developing embryo (and later fetus) until shortly before birth. The inner membrane, the amnion, contains the amniotic fluid and the fetus. The outer membrane, the chorion, contains the amnion and is part of the placenta.