Japanese secular trends in birthweight and the prevalence of low birthweight infants during the last three decades: A population-based study

Since low birthweight has been correlated with both neonatal and long-term health, we performed this epidemiological study to evaluate the Japanese secular trends in mean birthweight and the prevalence of preterm/term low birthweight infants during the last three decades. We used population-based birth certificate data from January 1979 to December 2010. Time trends were analysed using a linear regression model. During the study period, we observed a significant decrease in the mean birthweight for singleton live births (3,152 ± 436 g in 1979 and 3,018 ± 421 g in 2010 p < 0.001) and an increase in the prevalence of preterm/term low birthweight infants. A 96.3% increase in the proportion of term low birthweight infants was observed during the study period (2.7% in 1979 and 5.3% in 2010). In addition, an increased proportion of preterm/low birthweight infants born to younger women was observed (<35 years vs. ≥35 years). These trends may be related to changing patterns in Japanese women's nutritional status and the relatively strict recommended limit on weight gain during pregnancy. Understanding the long-term trends for singleton births may allow us to identify the associated risk factors and reduce the future socioeconomic burden that is associated with low birthweight infants.