Low lying placenta or placenta praevia
What is placenta praevia?
As your pregnancy progresses your womb expands and the area where the placenta (afterbirth) is attached stretches up and away from your cervix (the neck of the womb). Sometimes the placenta stays low in your womb, close to or covering the cervix. This is called low lying placenta or placenta praevia. Most women with low lying placenta at the 20 week scan do not have any problems during their pregnancy. However it is important that the position of the placenta is checked again later in the pregnancy.
Risk factors for placenta praevia
- Maternal age
- Previous caesarean section
- IVF pregnancy
- Previous surgery in your womb (e.g myomectomy, removal of fibroids)
- Multiple pregnancy (e.g twins)
- Previous placenta praevia
Placenta praevia can sometimes cause heavy bleeding during the pregnancy. If you have a persistent placenta praevia towards the end of your pregnancy it would normally advised that you have a caesarean birth. However, the distance between the edge of the placenta and the cervical opening can change quite a lot during the last few weeks of pregnancy. This is because the lower part of the womb grows at a faster rate than the upper part, so it is quite common for the placenta to move away from the cervix. Consequently it may not be possible to advise you on the best mode of delivery (vaginal or caesarean) until the last few weeks of your pregnancy.
If your 20 week scan shows that the placenta is low lying or covering the cervix then a repeat scan will be performed at around 32 weeks of your pregnancy. At the 32 weeks scan 90% of placentas would have moved away from the cervix. In 10% of cases the placenta remains low. Usually a repeat scan is performed at 36 weeks to re-check the location of the growth of your baby. This scan may have to be performed vaginally, especially if your placenta is on the back wall of the womb (posterior) as this gives much more accurate information than scanning through your tummy.
Further sources of information
RCOG - Patient information leaflet
Placenta praevia, placenta accreta and vasa praevia
What complications can affect the placenta