amniotic navel

例句：

1. 1. The amniotic sac is a protective layer that surrounds the fetus during pregnancy.
   羊膜囊是胎儿在怀孕期间周围的保护层。
2. 2. During labor, the amniotic sac expands to help facilitate delivery.
   分娩期间，羊膜囊会膨胀以帮助促进分娩。
3. 3. The amniotic sac contains fluid that helps nourish the fetus during pregnancy.
   羊膜囊含有液体，有助于妊娠期间滋养胎儿。