What Increases Your Risk

It is hard to predict who is at risk for preterm labor. Some women with risk factors do not have early labor. Others with no known risk factors do have early labor.

Preterm labor and preterm birth

Most premature births happen after naturally occurring, or spontaneous, preterm labor (as opposed to a medically necessary preterm birth, when the baby must be delivered as quickly as possible to prevent harm to mother or baby).

Experts say that spontaneous preterm labor is often the result of a combination of factors. Some of the most common medical risk factors for a spontaneous preterm birth are:

• Pregnancy with twins, triplets, or more. (Use of assisted reproductive technology (ART) or superovulation increases the risk of multiple pregnancy, which carries a high risk of premature birth and resulting medical complications.⁴)
• In vitro fertilization (IVF), a type of ART. IVF twins may be born earlier than naturally-conceived twins.⁴
• A past preterm delivery.
• Vaginal bleeding in the second trimester.
• Infection in the urinary or reproductive tract, including the vagina.
• Age younger than 18 years.
• Mother's low body weight for height (body mass index).
• Cigarette smoking during pregnancy.
• Frequent contractions.

Other factors that may increase your risk for premature labor include:

• Use of cocaine or methamphetamine.
• Too much amniotic fluid (polyhydramnios).
• A significantly shortened cervix, as seen on ultrasound.
• A cervix that doesn't stay tightly closed until near your due date (incompetent cervix).
• A new pregnancy within 3 months of the end of your last pregnancy.
• Previous surgery on your cervix, such as a cone biopsy. Having a loop electrosurgical excision procedure (LEEP) also raises preterm labor risk.⁵
• Low pre-pregnancy weight or low weight gain during pregnancy.
• Not eating a balanced diet.