Preterm labor can be caused by a problem involving the baby, the mother, or both. Often a combination of several factors is responsible. But in about 1 out of 3 preterm births, the cause isn't known.¹

Causes of preterm labor include:

• Being pregnant with more than one baby. Women who are pregnant with more than one baby have an increased risk of complications—both for the mother and the babies—and typically deliver early.
• Infection, which can trigger uterine contractions and preterm premature rupture of membranes (pPROM). This may include:
  • Infections that begin in the vagina, such as bacterial vaginosis (BV).
  • Infections that begin in the urinary tract, such as a urinary tract infection.
  • Gum disease.
• Placenta abruptio. This is the early separation of the placenta from the uterus.
• The use of drugs such as cocaine or methamphetamine.
• Problems with the uterus or cervix, such as:
  • A weak, thin cervix.
  • Fibroid growth.
  • An abnormally shaped uterus.