Role of multiple births in very low birth weight and infant mortality

OBJECTIVE: To determine the percentage of very-low-birth-weight (VLBW) infants (<1,500 g) and infant deaths attributable to multiple births in the general population and in women aged 35+. STUDY DESIGN: The year 2000 Massachusetts birth certificate database with linked births-deaths was examined. Etiologic fractions (EF) for VLBW and infant mortality attributable to multiples were calculated for the general population and the 35 + age group. The percentages of multiples occurring in the 35+ age group were calculated. Infant deaths due to congenital anomalies and "perinatal conditions" were calculated. RESULTS: There were 81,582 resident births in Massachusetts in 2000. Of them 4.3% were multiples. Of the 1,090 VLBW infants, 26.1% (95% CI: 23.5-28.8) were in twins and 7.7% (95% CI: 6.2-9.5) in higher-order multiples, yielding an EF of 30.8% for multiples in VLBW. In the 35+ age group, the multiple birth ratio was 6.6% (95% Cl: 6.3-7.0). The EF for multiples and VLBW in this age group was 33.7%. The 35+ age group accounted for 32.4% (95% CI: 30.8-34.0) of twins and 45.5% (95% CI: 39.1-52.0) of higher-order multiples born in 2000. Of the 392 infant deaths, 57 (14.6%; 95% CI: 11.2-18.4) were attributed to congenital anomalies, and 236 (60.2%; 95% CI: 55.2-65.0) to "perinatal conditions. "Multiples were responsible for 8 (14%; 95% Cl: 6.3-25.8) of deaths due to anomalies, and 73 (30.9%; 95% Cl: 25.1-37.3) due to "perinatal conditions." CONCLUSION: Over 30% of VLBW infants, nearly 20% of infant mortality and >30% of infant mortality due to perinatal conditions could be attributed to multiples. Multiple pregnancy is a significant public health problem.