Amniotic Membrane

What is the amniotic membrane?

The amniotic membrane is a thin, strong membrane that surrounds a fetus during pregnancy. Specifically, it’s the inside or inner layer of the amniotic sac, which is the enclosure that holds a fetus. The amniotic sac also contains amniotic fluid and an outer layer called the chorion. Together, these structures form a protective barrier for the fetus so it can grow and develop.

The amniotic membrane is sometimes called the amnion.

What does the amniotic membrane do?

The amnion plays a critical role in the health of the fetus’s amniotic sac. Without the amniotic membrane, an amniotic sac wouldn’t be able to form and expand, contain amniotic fluid and hold a growing fetus. This makes the amniotic membrane an essential part of the fetal development process.

The amniotic sac is responsible for cushioning a fetus and absorbing the shock from jolts or bumpy movements. The fluid inside the amniotic sac helps regulate the fetus’s temperature. It also helps them move freely, which is essential for musculoskeletal development. Without the amniotic membrane, the amniotic sac wouldn’t be able to perform those functions.

There’s growing research to suggest that the amnion offers healthcare providers new ways to treat different conditions. It has anti-inflammatory, anti-bacterial and anti-scarring properties. Healthcare providers are exploring ways to use the membrane instead of discarding it as waste. Some possible applications include:

• Ophthalmology: Possible uses include treatment for dry eye, burns and ulcers, or corneal diseases.
• Wound healing: The amnion has wound-healing factors to reduce scarring and inflammation. It can also promote tissue healing for ulcers or burns.
• Regenerative medicine: The amnion may have properties that stimulate tissue regeneration.

Is the amniotic membrane the same as the placenta?

No, the placenta is a separate structure that provides nourishment and oxygen to a fetus.

Where is the amniotic membrane?

The amniotic membrane is the inside layer of the amniotic sac. The amniotic sac is inside your uterus during pregnancy. The layer on top of the amnion (and closest to your uterine wall) is called the chorion.

What is the amniotic membrane made of?

You can think of the amniotic membrane as a skin-like barrier. The amnionic membrane is made up of three smaller layers. These three layers not only give the amniotic membrane its durability but also its flexibility:

• Epithelium: The top layer of the amnion contains a type of epithelial tissue called cuboidal epithelial cells. These cells are cube-like and have equal height, width and depth.
• Basement membrane: This is the middle layer of the amnion, which mainly serves to separate epithelial tissue and connective tissue.
• Stroma: The innermost and thickest layer made up of connective tissue. Connective tissue provides support and helps connect different organs and structures together. You have connective tissue virtually everywhere in your body.

Unlike other membranes in your body that form with your own tissues (such as mucous membranes), the amniotic membrane forms with fetal tissue. It develops from the chorion (the outer layer of the amniotic sac).

What does it look like?

The amniotic membrane is almost see-through. Your pregnancy care provider can see it on a prenatal ultrasound around six weeks of pregnancy.

What health conditions can affect the amniotic membrane?

Most pregnant people won’t hear about their amniotic membranes during pregnancy. If you do, it might be because you’re experiencing a condition that affects it. Some of those may include:

• Chorioamionitis: This is a bacterial infection of the amnion or chorion. Antibiotics treat it.
• Amniotic band syndrome: This happens when the amnion tears or ruptures, creating loose bands of tissue inside the amniotic sac. The tissue can tangle around the fetus and restrict blood flow to its limbs. Treatment involves using prosthetics at birth, physical therapy or surgery.
• Premature rupture of membranes (PROM): This is when your amniotic sac ruptures before 37 weeks of pregnancy. Your amniotic membrane also opens when your water breaks.