2022 Volume 71 Issue 1 Pages 77-86
Objectives: The proportion of low birth weight (LBW: less than 2,500 g) infants in Japan is increasing consistently. Recent studies have suggested associations between intrauterine development including LBW and an increased risk of chronic diseases, such as obesity, diabetes, and cardiovascular diseases throughout adult life. Further nationwide quantitative analysis is required to clarify the factors that determine the increase in the proportion of LBW infants and the effect on future health outcomes. To address these important issues, we aimed to analyze the factors related to LBW using Vital Statistics of live births between 1980 and 2015 in Japan.
Methods: All birth registry data from 1980, 1985, 1990, 1995, 2000, 2005, 2010, and 2015 (n = 9,743,319), stored in Vital Statistics, a database maintained by the Ministry of Health, Labor, and Welfare of Japan including information from the national census, were analyzed using SAS statistical software version 9.4.
Results: Analysis of the national census in Japan from 1980 to 2015 revealed that the largest risk factor for LBW was an increase in early term birth at 37 gestational weeks. The population attributable risk proportion at 37 weeks showed a two-fold increase from 11% to 22% when adjusted for maternal age, sex, birth order, and number of fetuses. Thus, the gestational duration exhibited a stronger relationship with LBW infants than other evaluated pregnancy-related factors.
Conclusion: While multiple factors could be involved in the increase in the prevalence of LBW, early full-term birth, as likely determined by medical interventions for delivery, such as induction of labor and caesarean sections, constitutes an important factor affecting LBW. A more precise analysis of perinatal medicine for pregnant women is required to reduce the prevalence of LBW.
