Factors associated with birthweight decline in Japan (1980-2004)

Area of Science:

• Reproductive Health
• Pediatrics
• Public Health

Background:

• Birthweight in Japan has shown a consistent decline for over three decades.
• This trend represents one of the most significant increases in low birthweight among OECD countries.
• The study investigates the underlying causes of this declining birthweight phenomenon in Japan.

Purpose of the Study:

• To identify the key determinants contributing to the observed decrease in neonatal birthweight in Japan.
• To analyze trends in birthweight and associated obstetrical variables over a 25-year period.
• To provide insights for public health interventions aimed at improving birth outcomes.

Main Methods:

• Utilized population-based birth certificate data from vital statistics, encompassing 40,968,266 neonates born between 1980 and 2004.
• Employed linear regression analysis to examine time trends and the influence of obstetrical variables on birthweight.
• Adjusted for factors including gestational age, gender, birth order, multiple gestations, and paternal age.

Main Results:

• A consistent decline in mean birthweight was observed from 1980 to 2004, with a yearly decrease of 8.07g, accelerating after 1985 and plateauing post-1999.
• Even after adjusting for gestational age, gender, birth order, multiple gestations, and fathers' age, the yearly decline persisted at 5.13g.
• These findings indicate that standard obstetrical factors do not fully account for the birthweight reduction.

Conclusions:

• The recent decline in Japanese neonatal birthweight is not solely explained by gestational age, gender, birth order, multiple gestations, or paternal age.
• Pre-pregnancy maternal body mass index (BMI) and maternal diet are identified as crucial factors requiring further investigation.
• Public health priorities should include reducing induced deliveries and enhancing the BMI and nutritional status of young women.