What causes preterm labor?

Updated: May 04, 2021
  • Author: Michael G Ross, MD, MPH; Chief Editor: Carl V Smith, MD  more...
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The exact mechanisms of preterm labor are largely unknown but are believed to include the following:

  • Decidual hemorrhage such as abruption and mechanical factors such as uterine overdistention from multiple gestation or polyhydramnios

  • Cervical incompetence (eg, trauma, cone biopsy)

  • Uterine distortion (eg, müllerian duct abnormalities, fibroid uterus)

  • Cervical inflammation as a result of, for example, bacterial vaginosis (BV) or trichomonas

  • Maternal inflammation/fever (eg, urinary tract infection)

  • Hormonal changes (eg, mediated by maternal or fetal stress)

  • Uteroplacental insufficiency (eg, hypertension, insulin-dependent diabetes, drug abuse, smoking, alcohol consumption)

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