Japan has a higher prevalence of low birthweight infants (LBW, 35 years of age. The rate for the 15–19 age group increased gradually, with no change point (APC = 0.60). These findings likely reflect changes in maternal and socio-environmental factors—such as increased maternal age, undernutrition, lower body mass index (BMI), and expanded use of assisted reproductive technology and perinatal care—and emphasize the importance of preconception care and maternal health care, including nutrition and life-course approaches, to reduce low birthweight risk.
Nonoyama et al. (2026) studied this question.