Placenta previa is a condition that occurs when the placenta remains low in the uterus and covers or lies next to the internal cervical os, the opening to the cervix. The cervix is the portion of the uterus that dilates during the first stage of labor allowing delivery of a baby.

This condition can cause bleeding that can become severe and result in serious complications, such as massive bleeding (hemorrhaging), premature birth and, in rare cases, death of the mother or baby. It occurs in approximately 1 in 200 births, according to the National Institutes of Health (NIH).

There are several types of placenta previa:

• Total placenta previa. The placenta covers the entire internal cervical os.
  
  
• Partial placenta previa. The placenta covers part of the internal cervical os.
  
  
• Marginal placenta previa. The placenta is near, but not covering, the internal cervical os.

The cause of placenta previa has not been identified, but some possible causes are scars in the uterine lining (endometrium) and an abnormally large placenta resulting from a multiple gestation. Risk factors include having had previous Caesarean sections (C-section) deliveries and uterine surgeries.

The most common symptom of placenta previa is painless vaginal bleeding during the second half of pregnancy. Some women experience spotting earlier in the pregnancy and some experience no symptoms at all.

Placenta previa is usually diagnosed with an abdominal ultrasound performed during a routine prenatal examination by an obstetrician-gynecologist (ObGyn). A transvaginal ultrasound or MRI (magnetic resonance imaging) may be performed to pinpoint the location of the placenta in the uterus.

Treatment for placenta previa varies depending on the severity of the bleeding, age of the fetus and other factors. Women who are experiencing little or no bleeding may be prescribed bed rest. Women with more severe bleeding are usually hospitalized. Most women with placenta previa give birth by C-section.