Objective: The aim of the study was to describe risk factors for neonatal death among twins born in South Carolina.
Study design: South Carolina publicly accessible live birth and infant death cohort files for live-born twins >500 g were reviewed for the years 1988 through 1993. Infants with lethal anomalies were deleted from the cohort before analysis. Risk factors for neonatal death were determined for the entire cohort and for the birth weight categories of 500 to 999 g, 1000 to 1499 g, 1500 to 2499 g, and >/=2500 g. Statistical comparisons were performed with the Mantel-Haenszel chi2 test and multivariate logistic regression.
Results: Of 7833 live-born twins, 263 (3.4%) died during the neonatal period. The mean birth weight was 2357 +/- 650 g (range 500-5358 g) at a mean gestational age of 35.7 +/- 3.5 weeks. Overall neonatal mortality rates were significantly increased (P <.001) for twins whose mothers were nonwhite (4.2 vs 2.8%), were <20 years old (6.0 vs 3.2%), or received no prenatal care (14.7 vs 3.1%). After we controlled for population characteristics with multivariate techniques, analysis revealed birth weight <2500 g and residence in the most populous urban areas to be associated with increased neonatal mortality rates. After stratification into birth weight categories, race was no longer a significant variable; in fact, nonwhite twins had a survival advantage at birth weights <1500 g, but this was not significant. Maternal age <20 years was associated with a higher neonatal mortality rate for infants with birth weights between 1500 and 2499 g. Absence of prenatal care significantly increased the neonatal mortality rate for twins >/=1500 g but not for those who were smaller. For infants weighing 500 to 999 g neonatal mortality rates were significantly lower at hospitals with >/=2000 deliveries/y than at hospitals with lower delivery volumes (P =.005).
Conclusions: Although the overall neonatal mortality rate for twins continues to improve, increased rates are still seen among blacks, teenagers, and women who receive no prenatal care. Twins between 500 and 999 g have significantly reduced neonatal mortality rates when delivered at hospitals with a high obstetric volume.