The amniotic sac protects the fetus. It is made up of membranous tissues and fluids and surrounds the fetus in the womb. It is also known as the bag of water that breaks or ruptures before the birth of the child. The baby is then released from the safety of the amniotic sac.
The amniotic sac serves the basic functions of providing cushioning for the fetus as it develops. The fluid within the amniotic sac controls the temperature around the fetus, staying at least one or two degrees higher than the mother’s own temperature. During the second and third trimester, the relatively small fetus can move freely within the womb because of the fluid. This is why expectant mothers often report the baby as continuously shifting and changing positions as it swims around.
The reasoning behind a water birth is based on the amniotic fluid. Some people believe that the baby should be welcomed through an environment that it is already used to. Amniotic fluid is almost like water, so water seems the most natural environment to use since the baby has been living in water for so long. At birth, the baby usually emerges free from the amniotic sac, but at times may be covered by parts of it called a caul which is washed off.
If a small injury occurs to the amniotic sac, it can reseal itself to stop leakage. Any rupture of the amniotic sac leads to a sudden rush of fluid from the mother which is a sign of impending labor.