Low Lying Placenta
In 5% of pregnancies at 19-21 weeks the placenta is situated low in the uterus either close to or covering the cervix. As pregnancy progresses however, the lower part of the uterus grows such that the placenta eventually becomes clear of the cervix. In fact, in 95% of cases the placenta will be clear of the birth canal by 37 weeks of pregnancy. If you placenta is low lying at the 20 week scan, your doctor will refer you for in late pregnancy to monitor location of the placenta.
In a small number of pregnancies the placenta remains low after 28 weeks. This is called placenta praevia. A placenta which is praevia may cause vaginal bleeding in later pregnancy. Also in some patients with placenta praevia, the baby may need to be delivered by Caesarean section.