1. the innermost membrane that encloses the embryo and fetus of mammals, birds, and reptiles, forming a fluid-filled sac
Usage: anatomy, biology

Examples

• The amnion protects the developing fetus by surrounding it with amniotic fluid.
• During pregnancy, the amnion expands as the baby grows.
• The amnion is one of several membranes that support fetal development.
• Doctors can examine the amnion during an ultrasound to check fetal health.
• The amnion ruptures during labor, releasing the amniotic fluid.