The placenta is the organ which transfers oxygen and nutrients from the mother’s blood into the baby’s blood. It is connected to the mother’s uterus over a wide surface area. The baby is connected to the placenta via the umbilical cord.

Ultrasound is used to determine the location of the placenta and its proximity to the cervix. It can change during the pregnancy for a number of reasons.

Usually the placenta positions itself at either the top or side of the uterus. But it’s always possible that the placenta will attach to the front of the stomach, a position known as an anterior placenta. If the placenta attaches to the back of the uterus, near your spine, this is known as a posterior placenta.

Typically, your doctor will check the position of your placenta during your mid-pregnancy ultrasound, which should take place between 18 and 21 weeks of pregnancy.