The Causes of Low Birthweight Among Term Singletons in Japan: National Database Analysis

Abstract

Background: Progress on reducing global low birthweight (LBW) prevalence has been insufficient. Although focus has been on preventing preterm birth, evidence surrounding LBW in term birth is limited. Japan has a higher LBW proportion despite a low preterm birth prevalence than other developed countries. The study aim is to examine LBW prevalence in term singleton birth and investigate their causes using a national database. Methods: Retrospective analysis was conducted on 852,351 babies born between 2013 and 2017 registered in the Japan Society of Obstetrics and Gynecology Successive Pregnancy Birth Registry System. Findings: Prevalence of LBW was 18·3%, and a third (35·7%) of LBW derived from singleton term pregnancy. Multiple logistic regression analysis indicated various factors to be independently associated with LBW in term babies. Modifiable maternal factors included pre-pregnancy underweight (adjusted odds ratios [aOR] 1·65, 95% confidence intervals [CI] 1·62-1·69), inadequate gestational weight gain (aOR 1·90, 1·86-1·94), and smoking during pregnancy (aOR 1·78, 1·71-1·85). Non-modifiable factors included younger maternal age, nulliparity, hypertensive disorder of pregnancy, pre-eclampsia, delivery at 37 gestational weeks, cesarean section, female offspring, and congenital anomaly. Interpretation: LBW in term singleton birth was as common as in multiple and preterm births in Japan. Factors causing LBW in term singletons were similar to those in preterm birth, including maternal malnutrition, suggesting that strategies to reduce preterm birth could be equally effective in preventing LBW in term pregnancy. Evaluating the status and monitoring progress within countries on this issue may contribute to the overall reduction of LBW worldwide. Funding: None to declare. Declaration of Interest: None to declare. Ethical Approval: This study was approved by the Ethics committee of the Keio University School of Medicine, Tokyo, Japan (No. 20190220, approved November 25, 2019) and the Clinical Research Review Board, Japan Society of Obstetrics and Gynecology, Tokyo, Japan, (No. 2019-15, approved September 14, 2020).