Its face and body look more like that of an infant at the time of birth. Although it weighs a little over 1 pound at this point, it is still very small. Role of the Amniotic Sac and Amniotic Fluid By about the 12th day after fertilization, there is an early beginning of the amniotic sac, where the fetus grows and develops during pregnancy. The baby rests inside the amniotic sac in the amniotic fluid. See the illustration on page 203.
Amniotic fluid has several important functions.
It provides an environment in which the baby can move easily. It cushions the fetus against injury. Amniotic fluid regulates temperature for the baby. It provides a way of assessing the health and maturity of the baby. Following the 24th week of pregnancy, the volume of amniotic fluid continues to increase as your due date approaches.