Low-lying placenta at 20 week scan

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This information will tell you about having a low-lying placenta and placenta praevia. If you have any further questions about this, you can ask your midwife.

The Placenta

The placenta develops together with the baby in your uterus during pregnancy. It attaches to the wall of your uterus and provides a connection between you and your baby. Oxygen and nutrients pass from your blood through the placenta into your baby’s blood. The placenta is delivered shortly after the baby is born and it is sometimes called the afterbirth.

What is a low lying placenta?

In some women, the placenta attaches low down in the uterus and may cover part of or all of the cervix (the neck of the womb). In most cases, the placenta moves upwards and out of the way as the uterus grows during pregnancy. For some women, however, the placenta continues to lie in the lower part of the uterus as the pregnancy progresses.

This condition is known as low-lying placenta, where the placenta is less than 20 mm from the cervix, or as placenta praevia if the placenta completely covers the cervix. Having a low-lying placenta at 20 weeks means you need to have a repeat ultrasound at 32 weeks to check the placental site again. Sometimes this involves doing an internal (transvaginal) ultrasound scan. Your uterus grows as your pregnancy progresses. In around 95% of women the placenta moves up into a safe position for birth, and no further checks are needed.

What happens if the placenta is still low-lying after 32 weeks scan?

If the placenta remains low-lying, you will have an additional scan at 36 weeks. If the placenta remains low at 36 weeks then you will see an obstetrician who will to decide the safest way to deliver the baby. Sometimes the 32 week scan will diagnose a condition called Placenta Praevia, when the placenta is covering the cervix. This condition is rare, only occurring in 1:200 women with a low lying placentas, and is more common in women who have had fertility treatment or previous c-section. At your 20 week scan we may suspect placenta praevia, but it cannot be confirmed until your 32 week scan. With placenta praevia there is a lower chance of the placenta moving in time for a safe vaginal delivery. Normally a caesarean delivery is advised as the placenta blocks the baby’s way out. Very occasionally hospital admission is advised to monitor the pregnancy. There is also a higher risk the baby may be born early (before 37 weeks).

If I have a low-lying placenta or placenta praevia, what should I look out for?

You should continue your daily activities as normal, unless advised otherwise.

You should try to avoid becoming anaemic during pregnancy by having a healthy diet and by taking iron supplements if recommended by your healthcare team. Your blood haemoglobin levels (a measure of whether you are anaemic) will be checked at regular intervals during your pregnancy.

Who can I contact with any questions or concerns?

Further information

Royal College of Obstetrics and Gynaecologists