A placenta previa is when a portion of the placenta lies over the opening of a woman’s cervix. This complicates approximately 1 in every 200 births, and if you have a previa there are a few important things you should know as it can affect how you deliver your baby.
A placenta previa can be seen during an ultrasound examination. The most updated terminology divides previas into two types: placenta previa (where the placenta can cover the whole cervix, or just a part of it) and low-lying placenta (where the placenta does not cover the cervix, but is within 2 centimeters of the cervical opening).
A placenta previa can be diagnosed at any time during pregnancy, but it is important to keep in mind that having a previa in the second trimester does not mean it will stay that way until you deliver. In fact, approximately 2-5 percent of women will have a previa early in the second trimester, but this number drops as women progress in their pregnancies.
If a previa is seen, your provider will likely recommend that an ultrasound is repeated around 32 weeks of gestation to see if it is persistent or if it has resolved. If it is still there, another ultrasound is usually done around 36 weeks of pregnancy. If you have a persistent placenta previa, you will need to deliver via Cesarean section, typically around 36 weeks’ gestation, though this timing may vary. One exception is a low-lying previa that is more than 1 centimeter away from the cervix; usually vaginal deliveries are acceptable in this group.
There are a few risk factors for developing a placenta previa: having had more pregnancies, older maternal age, smoking, a history of a previa, and having delivered previously via cesarean section. In fact, a woman who has had four or more C-sections has around a 10 percent chance of a previa!
The biggest problem seen with placenta previa is vaginal bleeding, which is usually painless. It can be small in amount or catastrophic, so it is important to notify your provider immediately if any bleeding is seen. To decrease the chance of this, your provider will advise you to not put anything in the vagina (that means sex is off limits, but vaginal ultrasounds are considered safe) and to limit strenuous aerobic exercise.
If you do have bleeding, depending on how much it is, how far along you are, and whether it is your first bleeding episode will help your provider determine if delivery is necessary. If not, you may need to be observed in the hospital until it you are considered stable for discharge. Some women will stay in the hospital until they deliver if the risk of bleeding again is too high.
Reviewed by Dr. Jen Lincoln, April 2020
- A placenta previa is when a portion of the placenta lies over a woman’s cervix.
- Placenta previa complicates about 1 in 200 births.
- If you are diagnosed with a placenta previa early in pregnancy, it has a high likelihood of resolving.
- The most common complication of placenta previa is painless vaginal bleeding.