Low-lying placenta
Bright red, pain free bleeding occurring in mid or late pregnancy or in labour as the cervix ripens and opens can indicate a low-lying placenta (placenta praevia) which occurs when the placenta implants in the lower part of the uterus; it is called a grade 3 or 4 if it is covering the cervix.
The bleeding is due to a shearing force between the placenta and the underlying blood vessels in the wall of the uterus. A placenta praevia may give rise to very severe and even dangerous bleeding in the later weeks. The baby’s growth is usually not affected because the bleeding is from the placental margin and the rest receives a normal blood supply. In the majority of cases a low placenta detected by an early scan will appear to move up during pregnancy as the uterus expands. The placental site is monitored by ultrasound and treatment usually necessitates delivery by caesarean section because the placenta prevents the baby’s head from entering the pelvis, and there can be heavy bleeding. The baby’s growth is not usually affected.