Conditions · Obstetrics and gynecology
Preterm labour and birth !
Preterm labour is labour that starts before 37 weeks of pregnancy. Preterm birth is the leading cause of death in children under five.
Updated 2026-11-01
Structures involved
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In embryology
- Gestational age vs fertilization age: how pregnancy is dated
- Fetal period: month 3 to birth
- Twins: dizygotic and monozygotic, chorionicity, twin–twin transfusion
- Fetal lung, kidney and brain maturation: what preterm birth interrupts
- Surfactant and fetal lung maturity
- Androgens, diethylstilbestrol and other hormones
Why it happens
- Arachidonic acid metabolites in inflammation, and the drugs that block them
- Parturition: onset and uterine contraction
What it is
Regular uterine contractions with progressive cervical change (dilation or effacement) before 37 completed weeks of gestation. Preterm birth is any birth before 37 weeks, whether it follows spontaneous labour, rupture of membranes or a medically indicated delivery.
Who gets it
WHO estimates that about 13.4 million babies were born preterm in 2020, with national rates between about 4% and 16%. Complications of preterm birth are the leading cause of death in children under five, and most of these deaths are preventable with simple, low-cost care. It is a priority of maternal and newborn health programmes in Colombia and Latin America.
Causes
- Intra-amniotic infection or inflammation (ascending infection from the vagina)
- Uterine overdistension (multiple pregnancy, polyhydramnios)
- Decidual haemorrhage or placental abruption
- Premature activation of the maternal or fetal stress axis
- Cervical insufficiency
- Medically indicated early delivery (preeclampsia, fetal growth restriction)
Risk factors
- Previous spontaneous preterm birth (the strongest risk factor)
- Short cervix on transvaginal ultrasound in mid-pregnancy
- Multiple pregnancy
- Urinary tract infection, asymptomatic bacteriuria, pyelonephritis, bacterial vaginosis and periodontal disease
- Previous cervical surgery (cone biopsy, excision)
- Maternal age under 18 or over 35, low body weight, short interval between pregnancies
- Smoking, substance use, poor access to antenatal care
Pathophysiology
Different triggers converge on a common pathway: inflammatory cytokines and prostaglandins ripen the cervix, increase myometrial oxytocin receptors and gap junctions, and weaken the fetal membranes. The uterus shifts from quiescence to coordinated contractions, cervical change follows, and labour progresses before the fetus is mature.
Classification
- Extremely preterm: before 28 weeks
- Very preterm: 28 to before 32 weeks
- Moderate to late preterm: 32 to before 37 weeks
- Spontaneous (labour or PPROM) versus provider-initiated preterm birth
Symptoms and signs
- Regular, often painful contractions or a tightening of the abdomen
- Menstrual-like cramps or dull low back pain
- Pelvic pressure
- Change in vaginal discharge: watery, mucous or blood-stained
- Leakage of fluid from the vagina
Diagnosis
- Clinical
- Confirmed by regular contractions plus documented cervical change on examination before 37 weeks. Gestational age is established, membranes are assessed by sterile speculum examination, and digital examination is avoided if rupture of membranes or placenta previa is suspected.
- Tests
- Fetal fibronectin in cervicovaginal secretions (a negative result makes delivery within 7–14 days unlikely); urinalysis and urine culture; vaginal and rectal swab for group B streptococcus; testing for infection when indicated. Continuous fetal heart rate and contraction monitoring.
- Imaging
- Transvaginal ultrasound of cervical length (a long cervix makes preterm birth unlikely), obstetric ultrasound for fetal presentation, estimated weight, amniotic fluid and placental position.
Differential diagnosis
- Braxton Hicks (false labour) contractions without cervical change
- Placental abruption
- Urinary tract infection or pyelonephritis
- Round ligament pain or musculoskeletal low back pain
- Appendicitis or other acute abdominal conditions in pregnancy
Goal of treatment
Gain time to give antenatal corticosteroids and transfer the mother to a centre with neonatal intensive care, protect the preterm baby's brain and lungs, prevent neonatal infection, and avoid prolonging pregnancy when continuing it is unsafe.
Treatment
- Medical
- Antenatal corticosteroids (betamethasone or dexamethasone) for women at risk of delivery between about 24 and 34 weeks, to speed fetal lung maturation and reduce brain haemorrhage and neonatal death.
- Medical
- Short-term tocolysis (for example nifedipine, an oxytocin receptor antagonist, or indomethacin before 32 weeks) to delay delivery for about 48 hours so that steroids and transfer can take effect; contraindicated with infection, abruption or fetal compromise.
- Medical
- Magnesium sulfate for fetal neuroprotection when birth is expected before about 32 weeks, which reduces the risk of cerebral palsy.
- Medical
- Antibiotic prophylaxis against group B streptococcus in labour when the status is unknown or positive; antibiotics are not used to stop labour with intact membranes.
- Procedure
- In selected women: vaginal progesterone when a short cervix is found, and cervical cerclage for cervical insufficiency or a history of preterm birth with a short cervix.
- Follow-up
- Nursing priorities: monitor contractions, fetal heart rate and maternal vital signs; watch for side effects of tocolytics and magnesium; prepare neonatal resuscitation and kangaroo mother care after birth.
Complications
- Respiratory distress syndrome and bronchopulmonary dysplasia in the newborn
- Intraventricular haemorrhage, periventricular leukomalacia and cerebral palsy
- Necrotising enterocolitis, neonatal sepsis and retinopathy of prematurity
- Hypothermia, hypoglycaemia and feeding difficulties
- Long-term learning, visual and hearing problems
- Neonatal death, highest in extremely preterm babies
Prognosis
Survival and long-term outcome depend mainly on gestational age at birth and on access to antenatal steroids and neonatal care. Most late preterm babies do well; extremely preterm babies have high mortality and disability, especially in low-resource settings. Women who had a preterm birth have a higher risk in later pregnancies.
Prevention
- Early and regular antenatal care with accurate dating by early ultrasound
- Screening and treating asymptomatic bacteriuria in pregnancy
- Stopping smoking and substance use; adequate spacing between pregnancies
- Progesterone or cerclage in selected women at high risk
Test yourself
Think of the answer, then tap the question to see it.
What defines preterm labour?
Regular contractions with cervical change before 37 completed weeks of gestation.
What is the strongest risk factor for spontaneous preterm birth?
A previous spontaneous preterm birth; a short cervix in mid-pregnancy is also a strong predictor.
Which intervention most improves neonatal outcome when preterm birth is expected before 34 weeks?
Antenatal corticosteroids, which speed lung maturation and reduce intraventricular haemorrhage and death.
Why is magnesium sulfate given before birth at less than 32 weeks?
For fetal neuroprotection: it lowers the risk of cerebral palsy.
What is the main purpose of tocolysis?
To delay delivery for about 48 hours so corticosteroids can act and the mother can be transferred.
Related conditions
- Premature rupture of membranes (PROM and PPROM)
- Preeclampsia
- Urinary tract infection (acute cystitis)
- Acute pyelonephritis
- Bacterial vaginosis
- Placental abruption
Educational information, not medical advice. For any symptom, see a health professional.
Sources: Preterm birth (World Health Organization, 2023); Preterm Labor (MedlinePlus (U.S. National Library of Medicine), 2024).
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