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What is placenta previa?
If you have placenta previa, it means that your placenta is lying unusually low in your uterus, touching or covering the cervical opening). When the edge of the placenta is within two centimeters of the cervix but not touching it, it's called low-lying placenta.
(The placenta is the pancake-shaped organ – normally located near the top of the uterus – that supplies your baby with nutrients through the umbilical cord.)
Is placenta previa dangerous?
It can be, if it persists.
Having placenta previa at your mid-pregnancy ultrasound isn't usually a concern. As your pregnancy progresses, your placenta is likely to "migrate" farther from your cervix so that it's no longer a problem.
(Since the placenta is implanted in the uterus, it doesn't actually move, but it can end up farther from your cervix as your uterus expands. Also, as the placenta itself grows, it's likely to grow toward the richer blood supply in the upper part of the uterus.)
If the placenta is still close to the cervix later in pregnancy, it can cause serious bleeding and may mean that you'll need to deliver early. If you have placenta previa when it's time to deliver your baby, you'll need to have a cesarean section.
About 1 in 250 women who give birth have placenta previa at the time of delivery.
How will I know if I have placenta previa?
The location of your placenta will be checked during your mid-pregnancy ultrasound exam (usually done between 18 and 22 weeks). If you're found to have placenta previa, you'll have a follow-up ultrasound in your third trimester to recheck the location of your placenta. Your healthcare practitioner may put you on "pelvic rest," which means no intercourse or vaginal exams for the rest of your pregnancy.
What are the symptoms of placenta previa?
Usually there are no symptoms. The most common symptom, though, is vaginal bleeding in the second half of pregnancy. The bleeding happens when your cervix begins to thin out or open up (even a little), which disrupts the blood vessels in that area. Ten to 20 percent of women with placenta previa also have uterine contractions and pain. If you have bleeding or contractions, go to the emergency room immediately.
By the way, if you have bleeding and you're Rh-negative, you'll need a shot of Rh immune globulin, unless the baby's father is Rh-negative, too.
What happens if I have placenta previa late in pregnancy?
When it's time to deliver, you'll need a c-section. With a complete previa, the placenta blocks the baby's way out. And even if the placenta is only bordering the cervix, you'll still need to deliver by c-section in most cases because the placenta can bleed profusely as the cervix dilates.
When you deliver will depend on how far along you are in your pregnancy, how heavy your bleeding is, and how you and your baby are doing.
Your baby will need to be delivered immediately if he's not doing well or if you have heavy bleeding that doesn't stop. Otherwise, you'll be watched in the hospital until the bleeding stops. You may be given medication to speed up your baby's lung development and to prevent other complications in case he ends up being delivered prematurely.
If the bleeding stops for at least a couple of days – and you and your baby are in good condition and you have quick access to a hospital – you may be sent home. But it's common for the bleeding to start again at some point and, when this happens, you'll need to return to the hospital immediately.
If you and your baby continue to do well, you'll have a scheduled c-section at around 37 weeks. When making the decision, your medical team will weigh the benefit of giving your baby extra time to mature against the risk of waiting, with the possibility of facing an episode of heavy bleeding and the need for an emergency c-section.
What complications can placenta previa cause?
Heavy bleeding. Having placenta previa makes it more likely that you'll have heavy bleeding and need a blood transfusion. This can even happen after the placenta is delivered because it was implanted in the lower part of the uterus, which doesn't contract as well as the upper part – so postpartum contractions aren't as effective at stopping the bleeding.
Placenta accreta. Women who have placenta previa are also more likely to have a placenta that's implanted too deeply and that doesn't separate easily at delivery. This is called placenta accreta and it can cause massive bleeding and the need for multiple blood transfusions at delivery. It can be life threatening and may require a hysterectomy to control the bleeding.
Premature birth. If you need to deliver before term, your baby will be at risk for complications from premature birth, such as breathing problems and low birth weight.
Future preterm birth. There's also some evidence that women with placenta previa who deliver preterm (especially before 34 weeks) are at increased risk for preterm birth in future deliveries.
Who's most at risk for placenta previa?
Most women who develop placenta previa have no apparent risk factors. But if any of the following apply to you, you're more likely to have it:
- You had placenta previa in a previous pregnancy.
- You've had c-sections before. (The more c-sections you've had, the higher the risk.)
- You've had some other uterine surgery (such as a D&C or fibroid removal).
- You're pregnant with twins or more.
- You're a cigarette smoker.
- You use cocaine.
- You've had in-vitro fertilization.
- You have an abnormally shaped uterus.
Also, the more babies you've had and the older you are, the higher your risk.
What is vasa previa?
In vasa previa, some of the fetal blood vessels are exposed and cross over the cervical opening, instead of being contained in the umbilical cord. When contractions happen, these blood vessels stretch and may rupture, resulting in catastrophic fetal blood loss and fetal distress. This is a very serious condition and may require prolonged monitoring in the hospital.