Fetal and neonatal mortality among twin gestations in the United States: the role of intrapair birth weight discordance.

OBJECTIVE

To examine the association of intrapair birth weight discordance with fetal and neonatal mortality.

METHODS

We used the United States (1995-1997) Matched Multiple Birth File (n = 297,155).

RESULTS

Among twin live births and stillborn fetuses, 29.9% had less than 5% birth weight discordance, 24.2% had 5-9%, 29.6% had 10-19%, 11.1% had 20-29%, 3.4% had 30-39%, and 1.8% had 40% or more. The stillborn fetus rate increased progressively with increasing birth weight discordance for smaller and larger twins of the same sex. Compared with the less than 5% birth weight discordance category, the adjusted odds ratios (OR) (95% confidence intervals [CIs]) for stillborn fetus associated with 5-9%, 10-19%, 20-29%, 30-39%, and 40% or more birth weight discordance, respectively, were 0.81 (95% CI 0.58, 1.11), 1.41 (95% CI 1.07, 1.84), 1.74 (95% CI 1.28, 2.35), 3.06 (95% CI 2.21, 4.24), and 4.29 (95% CI 3.05, 6.04) for smaller twins. The corresponding ORs (95% CIs) for larger twins were 0.78 (95% CI 0.57, 1.08), 1.26 (95% CI 0.96, 1.66), 1.77 (95% CI 1.27, 2.46), 3.38 (95% CI 2.33, 4.92), and 2.91 (95% CI 1.89, 4.47). Similar associations were observed among smaller but not larger twins of opposite sex. Among larger but not smaller twins of the same sex, increasing birth weight discordance was associated with overall neonatal deaths. This association was not apparent among smaller and larger twins of opposite sex. However, increasing birth weight discordance was associated with neonatal deaths related to congenital malformations among smaller and larger twins.

CONCLUSION

The results provide evidence that increased twin birth weight discordance was associated with increased risk of intrauterine death and malformation-related neonatal deaths.