Secular trends in the prevalence of small vulnerable newborns in Japan, 1997-2021.

BackgroundIn 2023, a collaborative UNICEF-WHO group introduced the concept of small vulnerable newborns (SVNs) to improve the identification of newborns at increased risk of adverse outcomes and to guide more effective preventive strategies. However, global data on the prevalence of SVNs remains scarce. This study aimed to examine secular trends in the prevalence of SVNs and their three subgroups, namely term small for gestational age (SGA), preterm SGA, and preterm non-SGA, in the Japanese population.MethodsWe analyzed data from vital statistics including livebirths and stillbirths between 1997 and 2021. Secular trends in the prevalence of SVNs and their subgroups were assessed. In addition, we conducted regional analyses to explore associations with the distribution of medical resources.ResultsA total of 26,172,760 newborns were included. The overall prevalence of SVNs was 7.8% in 1997, peaked at 8.7% in 2005, and declined to 7.7% by 2021. This decline was primarily attributed to a reduction in term SGA births. In contrast, the prevalence of preterm SGA and preterm non-SGA remained largely unchanged. In 2021, the prevalence of term SGA, preterm SGA, and preterm non-SGA was 2.0%, 0.44%, and 5.3%, respectively. No significant association was found between the regional variation in the prevalence of SVNs and the distribution of medical resources.ConclusionThe prevalence of SVNs in Japan has declined since 2005, mainly due to reduced term SGA births. Persistent rates of preterm subgroups highlight the ongoing burden of prematurity, underscoring the need for targeted strategies to improve neonatal outcomes.