August 29th, 2011 by Hasham

What is placenta previa?

If you have placenta previa, it means that your placenta is lying unusually low in your uterus, next to or covering your cervix. 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.

If you’re found to have placenta previa early in pregnancy, it’s not usually considered a problem. But if the placenta is still close to the cervix later in pregnancy, it can cause bleeding, which can lead to other complications 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.

If the placenta covers the cervix completely, it’s called a complete or total previa. If it’s right on the border of the cervix, it’s called a marginal previa. (You may also hear the term “partial previa,” which refers to a placenta that covers part of the cervical opening once the cervix starts to dilate.) If the edge of the placenta is within two centimeters of the cervix but not bordering it, it’s called a low-lying placenta.

The location of your placenta will be checked during your mid-pregnancy ultrasound exam (usually done between 16 to 20 weeks) and again later if necessary.
What happens if I’m diagnosed with placenta previa?

It depends on how far along you are in pregnancy. Don’t panic if your mid-pregnancy ultrasound shows that you have placenta previa. As your pregnancy progresses, your placenta is likely to “migrate” farther from your cervix and no longer be 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 placenta previa is seen on your second-trimester ultrasound, you’ll have a follow-up ultrasound early in your third trimester to recheck the location of your placenta. If you have any vaginal bleeding in the meantime, you’ll have an ultrasound to find out what’s going on.

Only a small percentage of women who have a low-lying placenta or previa detected on an ultrasound before 20 weeks still have it when they deliver their baby. A placenta that completely covers the cervix is more likely to stay that way than one that’s bordering it (marginal) or nearby (low-lying). Overall, placenta previa is present in up to 1 in 200 deliveries.

What Is Placenta Previa?

The placenta is the organ created during pregnancy to nourish the fetus, remove its waste, and produce hormones to sustain the pregnancy. The placenta is attached to the wall of the uterus by blood vessels that supply the fetus with oxygen and nutrition, and which remove waste from the fetus and transfer it to the mother.

The fetus is attached to the placenta by the umbilical cord. Through the cord, the fetus receives nourishment and oxygen and expels waste. On one side of the placenta, the mother’s blood circulates, and on the other side, fetal blood circulates. The mother’s blood and fetal blood usually don’t mix in the placenta.

The placenta is usually attached to the upper part of the uterus, away from the cervix, the opening which the baby passes through during delivery. On rare occasions, the placenta lies low in the uterus, partly or completely blocking the cervix — called a placenta previa.

Placentia previa may be observed in as many as one in every three pregnancies before the 20th week of pregnancy. As the uterus grows, the placenta usually moves higher in the uterus, away from the cervix. But if it remains near the cervix as your due date nears — which happens in about one in 200 pregnancies — you’re at risk for bleeding, especially during labor as the cervix thins (effaces) and opens (dilates). This can cause major blood loss in the mother. For this reason, women with a placenta previa are usually delivered by cesarean delivery.

There are several types of placenta previa:

* A low-lying placenta is near the cervical opening but not covering it. It will often move upward in the uterus as your due date approaches.
* A partial placenta previa covers part of the cervical opening.
* A total placenta previa covers and blocks the cervical opening.

What Causes Placenta Previa?

The cause of placenta previa is usually unknown, although it occurs more commonly among women who are older, smoke, have had children before, have had a cesarean section or other surgery on the uterus, or have scars inside the uterus.

Women with placenta previa — specifically if they have a placenta previa after having delivered a previous baby by cesarean section — are at increased risk of placenta accreta, placenta increta, or placenta percreta.

In placenta accreta, the placenta is firmly attached to the uterus. In placenta increta, the placenta has grown into the uterus; and in placenta percreta, it has grown through the uterus. This condition is often first suspected because the woman has both a previa and a prior cesarean section. It can be confirmed by ultrasound, CT scan, or MRI, though those tests are not completely reliable. Women with one of these conditions usually require a hysterectomy after delivery of the baby, because the placenta does not separate from the uterus.