The amniotic sac is a protective membrane that surrounds a developing fetus during pregnancy. It is filled with a clear fluid called amniotic fluid, which cushions the fetus and allows it to move freely. This fluid helps maintain a stable temperature and provides a safe environment for the baby to grow. As the pregnancy progresses, the amniotic sac plays a crucial role in supporting the fetus's development. It helps prevent injuries from external forces and allows for the proper formation of organs and limbs. When labor begins, the amniotic sac usually breaks, releasing the fluid, which is often referred to as the "water breaking."