amnion
Pronunciation: AM-nee-on
The innermost fetal membrane that directly surrounds the fetus and contains amniotic fluid.
Full Definition
The amnion is the thin, transparent innermost membrane of the amniotic sac that directly encloses the fetus and amniotic fluid. It is composed of a single layer of epithelial cells and plays crucial roles in maintaining fluid balance, preventing infection, and facilitating fetal movement. The amnion can be visualized on ultrasound and may show abnormalities such as amniotic bands or sheets. During labor, rupture of the amnion (along with the chorion) releases amniotic fluid and is commonly referred to as 'water breaking.'
Usage
Usage note: Often used interchangeably with 'amniotic sac' though technically the amnion is just the inner layer.
In Context
- "The amnion appeared intact on ultrasound with normal amniotic fluid volume." — Second trimester ultrasound report
- "Rupture of the amnion occurred spontaneously at 39 weeks gestation with clear fluid release." — Labor admission note