The foetus in the stomach is surrounded by two pieces of amniotic membrane that lie right next to each other – much like the thin membrane under the shell around a hen’s egg. As long as the amniotic membranes are intact, they protect the foetus by preventing bacteria from entering the uterus and the amniotic fluid from escaping.

The two membranes are called the chorion (choroid membrane) and the amnion (aqueous membrane). The chorion is the outermost membrane and the amnion is the one closest to the foetus and is adjacent to the amniotic fluid.

Amniotic membranes

The amniotic membranes help protect the foetus and the umbilical cord by keeping the pressure from the amniotic fluid evenly distributed inside the uterus, for example during contractions. By allowing the foetus to move in the amniotic fluid, it contributes to the development of the foetus’s muscles, bones and lungs.

At the beginning of pregnancy, the amniotic fluid is completely clear, but gradually the water becomes more cloudy due to the hairs, sebum and skin particles that the foetus has shed. Throughout pregnancy, new amniotic fluid is constantly being created. The foetus swallows amniotic fluid, which is then absorbed into the gastrointestinal tract. The outflow goes through the umbilical cord and the placenta into the pregnant woman’s blood circulation, but the foetus also excretes residues into the amniotic fluid. At around 38-39 weeks, the amniotic fluid volume reaches its highest level of around 1,000 ml, and then drops completely normally. It is possible to measure the amniotic fluid volume using ultrasound.

The umbilical cord

There are two arteries and a vein in the umbilical cord that help supply the foetus with oxygen-rich blood and remove carbon dioxide and waste products. The vessels are surrounded by a jelly-like structure made up of connective tissue. The umbilical cord is surrounded by the amniotic membrane and is attached to the placenta. It usually attaches centrally to the placenta, which you can see when the placenta comes out during childbirth.