During a normal pregnancy, your placenta will start low and slowly make its way up towards a richer blood supply. The placenta is the organ that connects your growing baby with your blood supply for the transfer of nutrients and waste removal. When your placenta moves up, it also makes way for your baby to leave the birth canal when it’s time for labor. However, some women’s placentas never make their way up, and this condition is called placenta previa.

Many women will have placenta previa early in the second trimester, so don’t panic if it shows up on an ultrasound. It simply means that your placenta has not moved up yet. Though, if it still sits at your cervix at the end of the second trimester, it might stay there for good, and medical intervention will be necessary.

Placenta previa occurs in less than 1% of pregnancies, but some women are at a higher risk. If you have an abnormally shaped uterus or scarring on your uterus, there’s a higher chance your placenta won’t move the way it’s supposed to. You’re also at a higher risk if you’re having twins or multiples, since there is less space in the uterus. Also, as with many pregnancy complications, you’re at a higher risk for placenta previa if you’re pregnant at an older age.

If your doctor hasn’t already noticed it in an ultrasound, you’ll notice placenta previa if your vagina starts bleeding heavily. Spotting is sometimes normal during your pregnancy, but you should call your doctor immediately if you are bleeding. Even if it’s not previa, blood could be a sign of a serious medical issue that puts you and your baby at risk.

Since the placenta is blocking the birth canal with placenta previa, nearly all women who have it will need a cesarean section. If they had a natural birth, they could easily bleed to death. If your doctor diagnoses you with placenta previa after week 36, he or she will probably recommend inducing labor so that you don’t lose any more blood. Blood transfusions are necessary for women who lose too much. If you do induce labor and have a cesarean section after your placenta previa diagnosis, your baby has a good chance of coming out happy and healthy. No birth defects are associated with the condition; the biggest complication associated with it are severe loss of blood from the mother.

Source: Matthew Weis et al: Natural History of Placenta Previa in Twins. Obstetrics and Gynecology Volume 120 Issue 4 pp. 753-758 October 2012

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