{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,8,23]],"date-time":"2026-08-23T17:12:22Z","timestamp":1787505142847,"version":"build-2736575974"},"reference-count":45,"publisher":"Public Library of Science (PLoS)","issue":"5","license":[{"start":{"date-parts":[[2021,5,20]],"date-time":"2021-05-20T00:00:00Z","timestamp":1621468800000},"content-version":"vor","delay-in-days":0,"URL":"http:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"DOI":"10.13039\/501100006120","name":"Ministry of the Environment","doi-asserted-by":"publisher","id":[{"id":"10.13039\/501100006120","id-type":"DOI","asserted-by":"publisher"}]}],"content-domain":{"domain":["www.plosone.org"],"crossmark-restriction":false},"short-container-title":["PLoS ONE"],"abstract":"<jats:p>The association between birth month and neurodevelopmental or psychiatric disorders has been investigated in a number of previous studies; however, the results have been inconsistent. This study investigated the association between birth month and child gross motor development at 6 and 12 months of age in a large cohort of infants (n = 72,203) participating in the Japan Environment and Children\u2019s Study (JECS). Gross motor development was assessed using the Ages and Stages Questionnaire (ASQ-3). At 6 months and 12 months, 20.7% and 14.2%, respectively, had ASQ-3 indications of gross motor problems. Birth month was strongly associated with gross motor development at both time points, particularly at 6 months. Summer-born infants had the worst outcomes at both 6 months and 12 months of age. This outcome applied to the ASQ-3 score itself and to the adjusted Relative Risk (aRR), with the highest aRRs (relative to January-born) among August-born (aRR 2.51; 95%CI 2.27\u20132.78 at 6 months), and June-born (aRR 1.84; 95%CI 1.63\u20132.09 at 12 months). Boys had better scores than girls both at 6 and 12 months of age. We speculate that seasonal factors\u2014such as maternal vitamin D deficiency and influenza infection\u2014affecting the fetus in early pregnancy might account for the findings.<\/jats:p>","DOI":"10.1371\/journal.pone.0251581","type":"journal-article","created":{"date-parts":[[2021,5,20]],"date-time":"2021-05-20T13:52:19Z","timestamp":1621518739000},"page":"e0251581","update-policy":"https:\/\/doi.org\/10.1371\/journal.pone.corrections_policy","source":"Crossref","is-referenced-by-count":9,"title":["Birth month and infant gross motor development: Results from the Japan Environment and Children\u2019s Study 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