Influence of mode of delivery on neonatal mortality in the second twin, at and before term.

DESIGN To study the association between mode of delivery and neonatal mortality in second twins. To study the association between caesarean delivery and mortality with minimum bias of the indication for the operation, we wanted to compare the outcome of second twins delivered by caesarean due to breech presentation of the sibling with vaginally delivered second twins in uncomplicated pregnancies. SETTING Sweden, 1980-2004. POPULATION Twins born during 1980-2004 were identified from the Swedish Medical Birth Registry. Twin pairs delivered by caesarean due to breech presentation of the first twin, and vaginally delivered twins with the first twin in cephalic presentation were included. Pregnancies with antepartum complications were excluded. METHODS Odds ratios and 95% CI were calculated using multiple logistic regression analyses, adjusting for year of birth, maternal age, parity and gestational age. MAIN OUTCOME MEASURES Neonatal mortality. RESULTS Compared with second-born twins delivered vaginally, second-born twins delivered by caesarean (for breech presentation of the sibling) had a lower risk of neonatal death (adjusted OR 0.40; 95% CI 0.19-0.83). The decreased risk after caesarean delivery was significant for births before 34 weeks (2.1 versus 9.0%; adjusted OR 0.40; 95% CI 0.17-0.95). After 34 weeks, neonatal mortality was low in both groups (0.1 and 0.2%, respectively), and the difference was not statistically significant (adjusted OR 0.42; 95% CI 0.10-1.79). CONCLUSIONS Neonatal mortality is lower for the second twin after caesarean delivery at birth before 34 weeks. At term, mortality is low irrespective of delivery mode.