Respiratory morbidity in late preterm twin infants

Antenatal corticosteroids have been shown to decrease neonatal respiratory morbidity in singleton pregnancies when given during the late-preterm period (34^0/7-36^6/7 weeks). Whether these findings also apply to late-preterm twins, who account for approximately one-third of infants born at 34^0/7-35^6/7 weeks, is currently unclear. The answer to this question depends, in part, on whether the risk of respiratory morbidity among late-preterm twin infants is similar to that observed in late-preterm singletons. We aimed to assess the rate of respiratory morbidity among late-preterm twin infants using a secondary analysis of prospectively collected data from a large international multicenter trial, and to compare that rate with previous studies that used the same definition of respiratory morbidity.

This was a secondary analysis of the twin birth study. In the current study, we limited the analysis to women who gave birth during the late preterm period. The primary outcomes were the same primary composite respiratory morbidity variables that were used in the randomized controlled trial of Gyamfi-Bannerman et al., on the administration of betamethasone during the late preterm period in singletons (ALPS trial). The risk of respiratory morbidity among late preterm twins was stratified by gestational week at birth.

A total of 1163 women who gave birth to 2324 late preterm twin infants met the inclusion criteria. The rates of respiratory morbidity and severe respiratory morbidity were 16.5% and 8.9%, respectively. The risk of respiratory morbidity was highly dependent on gestational week at birth, being more than fourfold for infants born at 34^0/7-34^6/7 weeks (aOR 4.30, 95%-CI 3.01-6.14) and more than twofold for infants born at 35^0/7-35^6/7 weeks (aOR 2.12, 95%-CI 1.51-2.98) compared with infants born at 36^0/7-36^6/7 weeks. The rate of respiratory morbidity and the theoretical number of women needed to be treated with betamethasone to prevent a single case of respiratory morbidity in the current study were similar to those reported in the APLS trial (16.5% vs. 14.4%, p = 0.103, and NNT 31 vs. 34, respectively).

The risk-benefit ratio of betamethasone with regard to neonatal respiratory morbidity in women with twins at risk of late-preterm birth is expected to be similar to that observed in singletons.