Risk of birth defects increased in multiple births

Previous studies inconsistently suggest that there may be an association between birth defects and multiple births.

Data were obtained from Zhejiang Hospital-Based Birth Defects Surveillance System during 2007 to 2009. There was a total of 545,018 pregnancies, including 537,593 singleton pregnancies, and 7425 multiple pregnancies (14,606 twins and 366 triplets). Odds ratio (OR)and confidence interval (CI) for birth defects were calculated for the singletons and multiple births.

The rate of birth defects in multiple births was 444.16 per 10,000 births versus 266.97 per 10,000 births in singletons (OR, 1.69; 95% CI, 1.57-1.84). A significant risk of birth defects was observed in 9 of 23 categories in multiple births. Both the multiple births and singletons with birth defects exhibited a similar proportion of single malformation, male children, and the mother living in a city. The multiple births with birth defects were delivered earlier (t = 7.90, p < 0.001) at a lower birth weight (t = 17.53, p < 0.001) compared to singletons with birth defects. The proportion of an antenatal diagnosis was higher in singletons compared with multiple births (p < 0.001). The multiple births with birth defects had a higher proportion of live birth and early neonatal death (p < 0.001).

An increased risk of birth defects in multiple births compared with singletons was confirmed.