amniotic

Amniotic is the adjective relating to the amnion, one of the fetal membranes that surrounds the developing fetus in the womb. The amnion forms the amniotic sac, which contains the amniotic fluid that cushions the fetus and supports its development.

During early embryogenesis the amnion derives from the inner cell layer (epiblast). Together with the chorion, it lines the gestational sac. By mid-pregnancy the amnion and chorion are typically fused into the surrounding chorioamniotic membranes. The amniotic cavity contains fluid that originates from maternal sources early on and increasingly from fetal urine and secretions as pregnancy progresses.

Amniotic fluid serves several functions. It provides buoyancy and permits fetal movement, protects the fetus from mechanical injury, and helps regulate its temperature. The fluid also facilitates lung development and gastrointestinal tract maturation through continual swallowing and fluid turnover. Fetal cells shed into the fluid provide material for prenatal testing.

Clinical relevance centers on variations in amniotic fluid volume. Oligohydramnios denotes too little fluid and can be linked to renal anomalies or placental insufficiency, while polyhydramnios is an excess and may occur with fetal or maternal conditions such as diabetes or certain congenital anomalies. Procedures involving the amnion include amniocentesis, a diagnostic sampling of amniotic fluid for fetal karyotyping or testing, and amniotomy, the artificial rupture of membranes to induce or expedite labor. Premature rupture of membranes can heighten infection risk and affect pregnancy outcome.