Risk factors

Preterm labor can affect any pregnancy. Many factors have been associated with an increased risk of preterm labor, however, including:

• Previous preterm labor or premature birth, particularly in the most recent pregnancy or in more than one previous pregnancy
• Pregnancy with twins, triplets or other multiples
• Shortened cervix
• Problems with the uterus or placenta
• Smoking cigarettes or using illicit drugs
• Certain infections, particularly of the amniotic fluid and lower genital tract
• Some chronic conditions, such as high blood pressure, diabetes, autoimmune disease and depression
• Stressful life events, such as the death of a loved one
• Too much amniotic fluid (polyhydramnios)
• Vaginal bleeding during pregnancy
• Presence of a fetal birth defect
• An interval of less than 12 months — or of more than 59 months — between pregnancies
• Age of mother, both young and older
• Black, non-Hispanic race and ethnicity