The Effect of an Increase in the Rate of Multiple Births on Low-Birth-Weight and Preterm Deliveries during 1975–2008

BACKGROUND: Despite the rapid increase in the rate of multiple births due to the growth of reproductive medicine, there have been no epidemiologic studies of the secular trends in the impact of multiple births on the rates of low-birth-weight and preterm deliveries in Japan. METHODS: Japanese vital statistics for multiple live births were obtained from the Ministry of Health, Labour and Welfare and reanalyzed. With singletons as the reference group, an analysis was performed of secular trends in relative risk and population attributable risk percent of low-birth-weight (<2500 grams), very-low-birth-weight (<1500 grams), and extremely-low-birth-weight (<1000 grams) deliveries, using 1975–2008 vital statistics, and of preterm deliveries (ie, before 37, 32, and 28 weeks), using 1979–2008 vital statistics. RESULTS: The rate of multiple births doubled during the past 2 decades, and about 2% of all neonates are now multiples. The population attributable risk percent tended to increase during the same period for all variables, and was approximately 20% in 2008. CONCLUSIONS: The public health impact of the rapid increase in multiple births remains high in Japan.