The placenta is a bed of cells formed inside the uterus (womb) during pregnancy. The purpose of the placenta is to carry nourishment and oxygen from the mother to the fetus and to carry waste products and carbon dioxide from the fetus to the mother through the umbilical cord.
The placenta is usually formed along the upper part of the uterus, allowing enough space for the fetus to grow. In placenta previa, the placenta starts forming very low in the uterus or even over the cervix (the opening of the uterus that leads to the vagina). This obstruction impairs normal vaginal delivery of the baby at birth.
There are 3 types of placenta previa:
Placenta previa is estimated to occur in 1 in 200 pregnancies.
The causes and risk factors for placenta previa are:
Slight and occasional bleeding may occur during the first and second trimester of pregnancy. The color of the blood may be bright red and it may start and stop, then restart after several days or weeks. Sudden and excessive bleeding may occur in the third trimester of pregnancy.
Bleeding is usually not accompanied by pain, although uterine cramping may occur at the time of bleeding in some women. In 7% to 30% of women there may be no bleeding at all.
The bleeding occurs because as the pregnancy progresses, the placenta gets detached from the uterine walls. In the third trimester the uterine walls become thinner and spread to accommodate the growing fetus. If placenta previa is present, the placenta is attached very low on the uterine wall. This thinning makes the placenta stretch and tear away from the uterine wall, leading to bleeding.
The following are the possible complications of placenta previa:
If you are diagnosed with complete placenta previa, your doctor will advise you to have a caesarean section for the delivery of your baby.