Preterm and term labour in multiple pregnancies.

The association between multiple pregnancy and preterm labour is well-established, with >50% of multiple births delivering before 37 weeks. However, there remains limited understanding of the factors predisposing to early delivery of twins. Physiological stimuli to the onset of parturition, including stretch, placental corticotrophin-releasing hormone and lung maturity factors, may be stronger in multiple pregnancies due to the increased fetal and placental mass. Pathological processes including infection and cervical insufficiency also have a role. Treatments that prevent preterm birth in singleton pregnancies, such as progesterone and cervical cerclage appear to be ineffective in multiple pregnancies. This article reviews aspects of preterm birth in twins and higher order multiples including epidemiology, prediction and prevention of preterm labour and potential mechanisms controlling onset of parturition. Evidence relating to the management of labour in preterm and term multiples is also discussed.