This can be picked up on an ultrasound scan as a low lying placenta in mid pregnancy. This is when the placenta is covering all or part of the entrance to the womb.If you are found to have a low lying placenta you will be rescanned between 32-36 weeks. The majority of low lying placentas will move to the upper part of the womb by 36 weeks, however 10% of low lying placentas remain low. This can cause bleeding in pregnancy that is sudden and severe. A caesarean birth may be recommended in cases of severe placenta praevia, and the likelihood of needing a blood transfusion can be higher.