Causes, incidence, and risk factors
Sometimes, though, the placenta remains in the lower portion of the uterus, partly or completely covering this opening. This is called a previa.
There are different forms of placenta previa:
- Marginal: The placenta is against the cervix but does not cover the opening.
- Partial: The placenta covers part of the cervical opening.
- Complete: The placenta completely covers the cervical opening.
- Abnormally developed uterus
- Many previous pregnancies
- Multiple pregnancy (twins, triplets, etc.)
- Scarring of the uterine wall caused by previous pregnancies, cesareans, uterine surgery, or abortions
- Abnormal formation of the placenta
- Abnormal uterus
- Large placenta
- Scarred lining of the uterus (endometrium)
There may be uterine cramping with the bleeding. Labor sometimes starts within several days after heavy vaginal bleeding. However, in some cases, bleeding may not occur until after labor starts.
- Major bleeding (hemorrhage)
Prematurity (infant is less than 36 weeks gestation) causes most infant deaths in cases of placenta previa. The baby may lose blood if the placenta separates from the wall of the uterus during labor. The baby also can lose blood when the uterus is opened during a C-section delivery.