Differences in outcome between twins and singletons born very preterm: results from a population-based European cohort.

Background: About 10% of twins are born before 32 weeks of gestation and very preterm birth rates are increasing. Preterm twins tend to have more favourable outcomes than singletons of the same gestational age, but fewer data are available for very preterm infants. This study aims to determine whether outcomes differ between very preterm twins and singletons.

Method: This study was of a population-based cohort of very preterm babies in 10 European regions in 2003. Mortality and morbidity to discharge from hospital were compared for twins and singletons between 24 and 31 weeks of gestation, who were alive at the onset of labour and without lethal congenital anomalies. Clinical characteristics, pregnancy complications and healthcare factors were taken into consideration.

Results: Between 28 and 31 weeks of gestation, mortality and oxygen dependency at 36 corrected weeks of gestation were lower for twins than singletons (3.9 versus 6.5% and 7.1 versus 10.4%, respectively), but this advantage disappeared after controlling for medical and healthcare factors. Hypertension, growth restriction and haemorrhaging were less frequent complications of twin birth and more twins received antenatal corticosteroids and were born in level III units. In contrast, between 24 and 27 weeks of gestation, twins had higher adjusted risks of mortality and Grade III/IV intraventricular haemorrhaging [adjusted ORs 1.5 (95% CI 1.1-2.2) and 1.5 (1.0-2.1)]. These adverse outcomes were concentrated among twins from same sex pairs with discordant birthweights.

Conclusions: Between 24 and 27 weeks of gestation, risks of mortality and severe cranial haemorrhaging were higher for twins than singletons if they were from same sex pairs with discordant birthweights.