What are the risk factors for spontaneous preterm labour?

• Previous preterm birth (strongest), previous cervical surgery (LLETZ/cone), cervical insufficiency
• Infection/inflammation - the cause of ~50% (UTI, bacterial vaginosis, chorioamnionitis)
• Uterine over-distension - multiple pregnancy, polyhydramnios
• Uterine anomalies, fibroids; smoking, low BMI, short inter-pregnancy interval; lower socio-economic status

Clinical relevance. Identifying risk factors (especially previous preterm birth and infection) targets prevention and surveillance.

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Risk factors for preterm labour

Identifying risk factors allows targeted prevention and surveillance.

Obstetric/cervical

• Previous preterm birth - the strongest predictor.
• Previous cervical surgery (LLETZ, cone biopsy) and cervical insufficiency (accounts for ~1% of preterm births).
• Uterine anomalies and fibroids.

Infection/inflammation

• Infection/inflammation underlies about 50% of preterm births - urinary tract infection, bacterial vaginosis, and chorioamnionitis.

Over-distension

• Multiple pregnancy and polyhydramnios.

Maternal/lifestyle

• Smoking, low BMI, short inter-pregnancy interval, lower socio-economic status, extremes of maternal age, and APH.

Mechanism

Whatever the cause, preterm birth results from premature cervical change (effacement/dilatation) with or without membrane rupture.