The placenta is an organ that connects the developing fetus to the wall of the uterus. It gets nutrients to the fetus, gets rid of waste, and allows oxygen exchange by means of the mother’s blood supply. The placenta usually moves up and away from the cervix (opening at the bottom of the uterus) during growth of the fetus. If it doesn’t, the cervix may be blocked. Placenta previa occurs when the placenta attaches to the uterine wall in the wrong spot, close to or covering the cervix. Placenta previa affects about 1 in 200 pregnancies. It’s a major cause of bleeding during pregnancy. It can be total, partial, marginal, or low-lying. In total placenta previa, the opening is fully covered. In partial placenta previa, the opening is partly covered. In marginal placenta previa, the edge of the placenta is at the edge of the opening. In low-lying placenta previa, the placenta attaches in the lower part of the uterus and its edge is close to the edge of the opening.
The cause is unknown. Risk factors include previous cesarean delivery, having been pregnant before, carrying twins or triplets, having had placenta previa or uterine surgery, age 35 or older, and smoking.
Most often, painless vaginal bleeding, usually in the second or third trimester, occurs. Uterine contractions may or may not be present. The uterus is soft and without pain. Fetal distress doesn’t usually occur.
The health care provider makes a diagnosis from the medical history and physical examination. Vaginal bleeding after 24 weeks of gestation is key. The best, safest way to find the place of attachment is by using ultrasonography. This test, using sound waves, can also tell whether delivery is needed. Magnetic resonance imaging (MRI) can also help detect the condition.
Treatment depends on the status of the fetus and of the mother. Fetal status and gestational age are checked by using the sonogram and continuous fetal heart rate monitoring. Outpatient treatment is possible for a fetus at less than 30 weeks of gestation, and if mother and fetus aren’t in distress. Placenta previa with a mature fetus or distress of the mother or fetus means immediate delivery. Cesarean delivery is done in almost all cases, especially for heavy bleeding. Vaginal delivery can be tried if the cervix is partly covered. Blood volume may need to be replaced to keep blood pressure normal. Blood transfusion may be done to replace lost blood. Levels of fibrinogen must be kept normal. Fibrinogen is a protein that’s important in clotting.
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Copyright © 2016 by Saunders, an imprint of Elsevier, Inc.
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