(HealthDay News) -- Pre-term labor occurs before the 37th week of pregnancy. About 10 percent of babies born in the United States are considered pre-term, the American Congress of Obstetricians and Gynecologists says.

The organization says these factors may increase the risk of pre-term labor:

  • Having had pre-term labor in this or a prior pregnancy.
  • Using cocaine or smoking cigarettes.
  • Having a multiple pregnancy (twins or more).
  • Having had a child born with a chromosomal disorder.
  • Having an abnormality in the cervix or uterus.
  • Having abdominal surgery during pregnancy.
  • Having an infection during pregnancy.
  • Bleeding during the second or third trimester of pregnancy.
  • Being underweight, or having insufficient prenatal care.
  • Having a mother or grandmother who took a drug called DES (diethylstilbestrol).