Amniotic sacs are what all of us have been in. They protect us from all the dangerous things inside our mother's stomach. If there was no amniotic sac formed during the birthing process a baby would not live. Having an infection inside the sac means the baby gets sick and wants to come out before it dies. This means you have a premature birth because the baby pushes out of the sac and when the baby comes out of the sac it has to come out of the mother.
"We only know the names of relatively a few of all the bacteria that exist, and a lot of them are difficult to culture or can't be cultured with our current technology," physician Robert Goldenberg tells us. Doctors think that in a woman's body the trigger for these bacteria are infection-causing microorganisms that live in the amniotic fluid. Even though all this information sounds like the bacteria and infections are linked to premature birth Dr. Daniel DiGiulio says that the studies have not yet confirmed that premature birth is linked to the infections and bacteria in the amniotic fluid.
http://www.sciencenews.org/view/generic/id/35826/title/Amniotic_sac_not_so_sacrosanct
http://dictionary.reference.com/browse/amniotic%20sac
by Mel