ArticleBMC public health2025
Impact of the COVID-19 pandemic on the monthly proportion of male births and spontaneous fetal death rates in Japan: a descriptive epidemiological study using national vital statistics.
Article in BMC public health, 2025. The graph could read no effect estimate from its abstract, so it casts no vote on the map. Not yet cited in PubMed.
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Abstract
backgroundA significant decrease in secondary sex ratio in December 2020 in Japan has been reported, suggesting the COVID-19 pandemic was a population-level stressor. However, few studies have investigated detailed trends in secondary sex ratio during the pandemic. This study aimed to describe the proportion of male births in Japan by month, mother's age and whether it was her first live birth, and suggest potential causes of anomalous variations during the COVID-19 pandemic, including variations in monthly spontaneous fetal deaths.
methodsJapanese national vital statistics data for 2006-2022 were used. Monthly proportion of male births by mother's age and whether it was her first live birth were analyzed. Spontaneous fetal death rates were also examined. Using a method similar to the [Formula: see text]-R control chart, anomalous variations in each indicator during COVID-19 were identified and the excess proportion of male births and excess spontaneous fetal deaths were estimated.
resultsAbnormal increases in the proportion of male births occurred in March 2020, November 2021 and June 2022, and a decrease in December 2020 and the biggest decrease in September 2021. These abnormal variations did not occur among first live births for mother's 20-29 and 40 or over, but there was an increase in March 2022 among subsequent live births for mother's 20-29, and decreases in March or April 2022 among all first live birth groups except women 20-29. Decreases occurred in October-December 2022 among first live births for all mother's up to 39, and increases in at least one month each of June-August, or December 2022 among the same age groups for subsequent live births. Spontaneous fetal deaths increased abnormally only in August 2022.
conclusionsAbnormal increases in spontaneous fetal deaths could not explain male birth proportion decreases. Abnormal decreases in proportion of male births occurred approximately 8-10 months after Japan's state of emergency declarations, but not 8-10 months after stimulus payments among groups with targeted families. Financial support might therefore have prevented decreases in the proportion of male births during states of emergency, but analytical studies are needed to test this hypothesis.
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