When you go for your 20 week scan one of the things that will be noted down is the position of the placenta. ⠀⠀ The entrance to the womb is known, in clinical terms, as the OS. It is not uncommon at this early stage for the placenta to be lying over this opening. When this does occur it is known as a low-lying placenta or placenta previa. ⠀⠀ In the vast majority of cases (90%) as the womb expands to house the growing baby the placenta is drawn up and away from the OS resulting in the all clear for a vaginal delivery. If the placenta remains in a low position you are more likely to experience bleeding during the pregnancy as the baby is lying on top of the organ. ⠀⠀ Bleeding can be heavy and significant, so it is important that you telephone the hospital immediately so that you can be monitored. ⠀⠀ If the placenta continues to block the exit route it is not possible for the baby to be born vaginally and a caesarean section will be recommended.