Introduction
Preterm birth is birth between 22⁺⁰ (or 24⁺⁰) and 36⁺⁶ weeks. It affects about 5–10% of births and is the leading cause of neonatal death and long-term disability.
Risk factors
- Previous preterm birth (strongest), short cervix on ultrasound (< 25 mm at 16–24 weeks).
- Multiple pregnancy, polyhydramnios, uterine anomalies, cervical surgery (cone biopsy).
- Infection: chorioamnionitis, bacterial vaginosis, asymptomatic bacteriuria, periodontal disease.
- Bleeding, preterm prelabour rupture of membranes (PPROM), smoking, low BMI, young age, social deprivation.
- Iatrogenic delivery for preeclampsia or fetal growth restriction.
Diagnosis
Regular painful contractions with cervical change before 37 weeks. Transvaginal cervical length and fetal fibronectin help: a cervix > 30 mm or a negative fibronectin makes delivery within a week unlikely.
Management of threatened preterm labour
Tocolysis is contraindicated in chorioamnionitis, fetal death or lethal anomaly, fetal distress, severe preeclampsia and significant bleeding.
Prevention
- Vaginal progesterone for a short cervix or previous preterm birth.
- Cervical cerclage for cervical insufficiency or a short cervix with a previous preterm birth.
- Treat asymptomatic bacteriuria; stop smoking.