Although the exact cause of placenta previa is not known, there are several possible causes that have been identified by health experts. These include:

• Scars in the endometrium, the lining of the uterus
• Large placenta, commonly found in women having multiple births
• Unusually shaped uterus
• Abnormally formed placenta

Several risk factors for placenta previa have been identified. These include:

• Past incidence of placenta previa. Women who have experienced the condition in past pregnancies are more likely to experience it again.
  
  
• Age. Women ages 35 and older have a higher incidence of placenta previa.
  
  
• Past Caesarean sections (C-sections). The more C-sections (removal of the fetus through an incision made through the uterus and usually through the abdominal wall) a woman has, the greater the incidence of placenta previa.

• Multiple gestations. Women carrying twins, triplets or more babies are more apt to have placenta previa because of a larger placenta.
  
  
• Multiple pregnancies. The more children a woman has, the greater the likelihood of developing placenta previa with future pregnancies.
  
  
• Previous operations on the uterus. Past surgeries, such as surgery to remove uterine fibroids (e.g., myomectomy) or dilation and curettage (D&C). This is a procedure in which the entrance to the woman’s uterus is expanded and tissue samples are removed from the uterine lining. Physicians commonly perform a D&C procedure after a miscarriage or a medical abortion.
  
  
• Cigarette smoking. Smoking decreases the amount of oxygen to the fetus, causing a larger placenta to grow. A larger placenta is more likely to grow low in the uterus.
  
  
• Cocaine use. Women who use cocaine during pregnancy are more apt to develop placenta previa.
  
  
• High altitude. Women who live in high-elevation areas have a greater incidence of placenta previa.
  
  
• Male fetus. Women carrying boys are more likely to develop placenta previa. This may be due to the typically larger size of a male fetus.

In addition, women who use assisted reproductive technology (ART), such as in vitro fertilization (IVF), to achieve pregnancy may be at increased risk of developing placenta previa, according to a recent large-scale study.