Placenta previa is a complication which emerges in around one in every 200 pregnancies carried to term. It is created when the placenta implants itself too close to the cervix, sometimes even partially covering the cervical opening. As the uterus and cervix undergo changes in the late stages of pregnancy to prepare for birth, breakthrough bleeding can occur, and if the placenta previa is still present at the onset of labor, vaginal birth can be very dangerous.
There are three different kinds of placenta previa: marginal, partial, and complete. Marginal placenta previa happens when the placenta is close to the cervix, but it doesn't cover it. The partial and complete types, as their names imply, partially or completely cover the cervix.
In the first 20 weeks of pregnancy, placenta previa is sometimes diagnosed on a prenatal ultrasound. While it is something to watch for, it is not something to worry about just yet, because sometimes the placenta grows into the upper part of the uterus, where the blood supply is more plentiful, and the problem resolves on its own. If this condition is diagnosed in the second half of pregnancy, however, it can be a cause for concern.
Sometimes, a doctor notices the problem on a routine ultrasound, and at other times, it is diagnosed after an expecting mother reports painless bleeding or spotting. Because the time of delivery is so much closer, risks for the mother and baby can increase. Women are usually put on pelvic rest, which means no pelvic exams or intercourse, and they may be encouraged to avoid heavy lifting. If breakthrough bleeding and placenta previa persist into the end of the third trimester, a mother may be put on bed rest.
If placenta previa is present at the time of delivery, most doctors will recommend a Cesarean section, which will allow them to be get the baby or babies out safely with a reduced risk of hemorrhage. In the event that breakthrough bleeding is severe in the last weeks of pregnancy, an immediate C-section may be required, even if the baby will be premature. The mother may require blood transfusions to compensate for the loss of blood, and she will have to be monitored after the birth to ensure that the bleeding has fully stopped.
Several factors can increase the risk of placenta previa, including age, smoking, a history of having the condition, twins and other multiples, and previous births. Like other complications of pregnancy, this one is entirely out of the mother's control, although she can reduce some risk factors, which is why routine prenatal care to check for complications and potential problems with delivery is so important.