Preterm birth

Delivery of a viable fetus before 37 completed weeks of gestation (fewer than 259 days from the first day of the last menstrual period), irrespective of birth weight or whether labor begins spontaneously or is medically initiated.

Causes and risk factors

• Spontaneous preterm labor

  • Previous preterm birth

  • Short cervical length or cervical insufficiency

  • Premature rupture of membranes (PPROM)

  • Uterine overdistension (multiple pregnancy, polyhydramnios)

  • Uterine abnormalities (Müllerian anomalies)

  • Maternal stress and psychosocial factors

  • Heavy physical workload

• Maternal medical conditions

  • Hypertensive disorders of pregnancy (preeclampsia, chronic hypertension)

  • Diabetes mellitus

  • Thyroid disorders

  • Autoimmune diseases (systemic lupus erythematosus)

  • Chronic kidney disease

  • Severe maternal illness

• Infections and inflammation

  • Bacterial vaginosis

  • Urinary tract infections

  • Sexually transmitted infections

  • Chorioamnionitis

  • Intra-amniotic infection

  • Periodontal disease (associated risk factor)

• Placental and fetal causes

  • Placental abruption

  • Placenta previa

  • Fetal growth restriction

  • Fetal congenital anomalies

• Obstetric and iatrogenic causes

  • Medically indicated early delivery due to maternal or fetal complications

  • Induction of labor or cesarean delivery before term

  • Assisted reproductive technology pregnancies (associated with higher risk)

• Lifestyle and environmental factors

  • Tobacco smoking

  • Alcohol or illicit drug use

  • Low maternal body weight or poor nutrition

  • Short interpregnancy interval

  • Advanced or very young maternal age

  • Exposure to environmental toxins