Placenta previa
Your placenta – which serves as your unborn baby’s life support system, supplying him with oxygen and nutrients and removing waste products – begins to form soon after the fertilized egg implants in the uterus. Just where it forms has implications for your labor and your baby’s safe birth.
What is placenta previa?
Ideally the
placenta should form high up in the uterus, well away from the cervix (neck of the uterus), which is your baby’s route out once labor starts. But occasionally, it attaches itself to the lower part of the uterus, near to the cervix. Usually it doesn’t cause a problem because as your uterus stretches and grows to accommodate your developing baby, it effectively ‘pulls’ the placenta repositions further up and away from the cervix.
Placenta previa is usually identified during your first ultrasound scan, long before it might cause problems. Your OB-GYN will monitor the situation to check that the placenta moves up. If it doesn’t, and it remains close to or covering the cervix, it’s known as placenta previa, and there are three different types:
- Total The placenta completely covers the cervix.
- Partial The placenta partly covers the cervix.
- Marginal The placenta approaches the edge of the cervix.
The term ‘low-lying placenta’ is also used to describe placenta previa but in this case the placenta isn’t close enough to the cervix to be considered marginal placenta previa. A low-lying placenta typically doesn’t cause problems during pregnancy, but may cause bleeding after the birth.
Who is at risk of placenta previa?
Placenta previa is more likely if you’ve previously had a
cesarean because the placenta has a tendency to attach to the area where the incision is, which will usually be low down in your uterus. It’s also more common in women who’ve had placenta previa with a previous pregnancy, and with
second and subsequent babies. Women who are older than 35, who have a large placenta (such as those who are expecting
twins) and those with an abnormally shaped uterus, also are at higher risk.
How will it affect my pregnancy?
If you have placenta previa but little or no bleeding, your OB-GYN or midwife may recommend bed rest. It’s likely they also will advise you not to have sex, to lessen the risk of bleeding, and as an extra safeguard, they won’t perform any vaginal exams. Exercise is off-limits, too.
However, even with these safety precaution, it’s common for women with the condition to experience bright red vaginal
bleeding in later pregnancy, typically around the end of the second trimester (weeks 13-28) and the beginning of the third (weeks 29-40). The bleeding may be heavy, but you won’t feel any pain, although some women do experience mild contractions with placenta previa. If you experience any bleeding, call your OB-GYN or midwife straightaway as they will likely want to carry out an
ultrasound to check the source of the bleeding.
How will it affect the birth?
Depending on how close to the cervix your placenta has implanted, the condition can prove very risky once your labor starts. This is because the
contractions that dilate the cervix could cause the placenta to detach from the wall of the uterus, causing severe bleeding and decreasing the supply of oxygen to your baby. The position of your placenta will be verified before you go into labor and your baby will need close monitoring.
If you have ongoing bleeding and contractions, you’ll be given medications to prolong your pregnancy for as long as possible, but your baby may need to be delivered prematurely, by cesarean section, if he is in distress. If you bleed heavily you may be given a blood transfusion.
The information in this feature is intended for educational purposes only. If you have any concerns about your health, the health of your child or the health of someone you know, please consult with a doctor or other healthcare professional.
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Last Modified: 20/12/2008
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