amniotic head fold

例句：

1. 1.The amniotic sac is a protective layer that surrounds the fetus during pregnancy.
   羊膜囊是怀孕期间围绕胎儿的保护层。
2. 2.During labor, the amniotic sac can expand and contract to help with delivery.
   在分娩过程中，羊膜囊可以扩张和收缩以帮助分娩。
3. 3.In some cases, an amniotic sac rupture may occur, leading to complications for both mother and child.
   在某些情况下，羊膜囊破裂可能发生，给母亲和孩子带来并发症。