Placenta previa (praevia) and low-lying placenta: what your scan means
In this article
Placenta previa, also spelled placenta praevia, is when your placenta completely covers the cervix, the opening of your womb. If it sits less than 2 cm from the cervix without covering it, that is a low-lying placenta. Both are usually spotted at the 20-week scan, and the NHS says that in 9 out of 10 pregnancies the placenta has moved up by about 32 weeks.
| Low-lying placenta | Edge less than 2 cm from the cervix (RCOG, NHS) |
|---|---|
| Placenta praevia | Completely covers the cervix |
| First seen | At the 20-week scan |
| Recheck | Scan at about 32 weeks; 9 in 10 have moved up (NHS) |
| Still there at the end | About 1 in 200 births (NHS, RCOG) |
Low-lying placenta at 20 weeks: what happens next
If your 20-week scan says the placenta is low, the odds are on your side. RCOG says that in most cases the placenta moves upwards and out of the way as the womb grows. The NHS says 9 out of 10 have moved into the upper part of the womb by the follow-up scan at about 32 weeks, and RCOG says only 1 in 200 women have placenta praevia at the end of pregnancy.
If it is still low at 32 weeks, RCOG says you should be offered another scan at 36 weeks. These checks may include a transvaginal scan, with the probe placed gently inside the vagina, which RCOG says is safe for you and your baby. A placenta is less likely to move up if you have had a caesarean before.
The warning sign: painless bleeding
RCOG says bleeding from placenta praevia is usually painless and may happen after sex. The NHS describes painless, bright red bleeding from the vagina in the last 3 months of pregnancy, and says it can be very heavy. KKH, via SingHealth, says bright red bleeding that comes and goes late in pregnancy could be from a low-lying placenta.
If you know your placenta is low, RCOG says contact the hospital straight away if you have any bleeding, contractions or pain. In Singapore, that means going to your delivery hospital or calling your gynae's clinic, not waiting for your next appointment.
Daily life with a low-lying placenta
KKH, via SingHealth, says to ask your doctor about sex if you have a low-lying placenta, because they may suggest a break from it. KKH also lists a low-lying placenta as a relative reason not to fly and asks you to get a medical check before air travel.
RCOG suggests you try to avoid becoming anaemic, with a healthy diet and iron tablets if your team recommends them, and says your haemoglobin will be checked regularly.
Giving birth with placenta praevia
A placenta over or near the cervix blocks the way out, so the NHS says a caesarean is recommended. RCOG puts the line at 20 mm on the 36-week scan: closer than that and a caesarean is the safest way to give birth; further away and you can choose a vaginal birth. Unless you have heavy or repeated bleeding, RCOG says the caesarean usually takes place between 36 and 37 weeks.
RCOG says placenta praevia raises the chance of your baby being born early, before 37 weeks (premature). You may be offered steroid injections between 34 and 36 weeks to help your baby mature. You are also more likely to need a blood transfusion, so blood is kept ready during the caesarean. RCOG adds that placenta praevia may be suspected when a baby is lying in an unusual position, such as breech.
Frequently asked questions
What is the difference between a low-lying placenta and placenta praevia?
Distance. RCOG calls it a low-lying placenta when the edge is less than 20 mm from the cervix, and placenta praevia when the placenta completely covers the cervix.
What causes placenta praevia?
RCOG says it is more common if you have had one or more caesareans, needed fertility treatment to get pregnant, or smoke.
Can I fly with a low-lying placenta?
Check with your doctor first. KKH lists a low-lying placenta as a relative contraindication to flying and says you should get a medical assessment before air travel.
Will I definitely need a caesarean?
Only if the placenta is still close to the cervix late in pregnancy. RCOG says a caesarean is safest if the edge is under 20 mm from the cervix on the 36-week scan, and that you can choose a vaginal birth if it is further away.
Related terms
- C-section (Caesarean Section): An operation to deliver your baby through a cut in your tummy and womb, planned ahead or done in labour.
- Breech: When your baby lies bottom first or feet first in the womb instead of head down near the end of pregnancy.
- Anaemia: Too few healthy red blood cells or too little haemoglobin, most often from low iron during pregnancy.
- Preterm (Premature) Birth: A baby born alive before 37 completed weeks of pregnancy. In Singapore, about 8.5% of babies arrive this early.
- Antenatal (also Prenatal): Antenatal means before birth. Antenatal care is the check-ups, scans and tests you get while you are pregnant.
- Trimester: One of the three stages of pregnancy, each about three months long.
