{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,1,7]],"date-time":"2026-01-07T05:48:25Z","timestamp":1767764905221,"version":"3.48.0"},"reference-count":34,"publisher":"BMJ","issue":"1","license":[{"start":{"date-parts":[[2026,1,6]],"date-time":"2026-01-06T00:00:00Z","timestamp":1767657600000},"content-version":"unspecified","delay-in-days":5,"URL":"https:\/\/creativecommons.org\/licenses\/by-nc\/4.0\/"}],"funder":[{"name":"the Central High-level Hospital Clinical Research Services","award":["2022\u2010PUMCH\u2010A\u2010015"],"award-info":[{"award-number":["2022\u2010PUMCH\u2010A\u2010015"]}]},{"name":"STI2030","award":["MajorProjects2021ZD0200500"],"award-info":[{"award-number":["MajorProjects2021ZD0200500"]}]}],"content-domain":{"domain":["bmj.com"],"crossmark-restriction":true},"short-container-title":["BMJ Open"],"accepted":{"date-parts":[[2025,12,6]]},"published-print":{"date-parts":[[2026,1]]},"abstract":"<jats:sec>\n                    <jats:title>Objective<\/jats:title>\n                    <jats:p>Maternal thyroid function affects fetal birth weight and age is an important factor in regulating thyroid function. Thus, we aimed to explore the association between age-specific preconception thyroid-stimulating hormone (TSH) and birth weight.<\/jats:p>\n                  <\/jats:sec>\n                  <jats:sec>\n                    <jats:title>Design<\/jats:title>\n                    <jats:p>Cohort study.<\/jats:p>\n                  <\/jats:sec>\n                  <jats:sec>\n                    <jats:title>Participants<\/jats:title>\n                    <jats:p>A total of 97\u2009755 preconception Chinese women aged 20\u201339 years old from the National Free Preconception Checkups Project were included.<\/jats:p>\n                  <\/jats:sec>\n                  <jats:sec>\n                    <jats:title>Setting<\/jats:title>\n                    <jats:p>Participants were divided into four age groups: 20\u201325 years, 25\u201329 years, 30\u201334 years and 35\u201339 years. The preconception TSH levels within 6\u2009months before pregnancy and fetal birth weight, including large for gestational age (LGA), small for gestational age (SGA) and appropriate for gestational age (AGA), were collected and analysed using restricted cubic spline regression. Logistic regression investigated the relationship between various TSH groups and birth weight.<\/jats:p>\n                  <\/jats:sec>\n                  <jats:sec>\n                    <jats:title>Results<\/jats:title>\n                    <jats:p>(1) Preconception TSH levels differed among four age groups; (2) in the 20-24 years group, preconception TSH was associated with the incidence of LGA and AGA (p&lt;0.001). The TSH range for OR of LGA lower than 1.0 was 1.32\u20132.12 mIU\/L and OR of AGA higher than 1.0 was 1.80\u20132.06 mIU\/L; (3) there were no significant associations between age-specific TSH and risks of LGA, SGA or AGA in the 25\u201329 years, 30\u201334 years and 35\u201339 years groups; (4) compared with TSH 1.32\u20132.12 mIU\/L, lower (&lt;1.32\u2009mIU\/L) and higher (&gt;2.12\u2009mIU\/L) TSH were associated with a higher risk of LGA and lower incidence of AGA in 20\u201324 years.<\/jats:p>\n                  <\/jats:sec>\n                  <jats:sec>\n                    <jats:title>Conclusion<\/jats:title>\n                    <jats:p>Preconception TSH exhibited a significant association with LGA and AGA in the 20\u201324 years age group, but not in the 25\u201339 years age group. Young preconception women should not neglect paying attention to their thyroid function, associated with the risk of LGA.<\/jats:p>\n                  <\/jats:sec>","DOI":"10.1136\/bmjopen-2025-105393","type":"journal-article","created":{"date-parts":[[2026,1,7]],"date-time":"2026-01-07T05:15:46Z","timestamp":1767762946000},"page":"e105393","update-policy":"https:\/\/doi.org\/10.1136\/crossmarkpolicy","source":"Crossref","is-referenced-by-count":0,"title":["Association between age-specific preconception thyroid-stimulating hormone (TSH) and birth weight: a retrospective study"],"prefix":"10.1136","volume":"16","author":[{"given":"Xi","family":"Bai","sequence":"first","affiliation":[{"name":"Key Laboratory of Endocrine Glucose & Lipids Metabolism and Brain Aging, Ministry of Education; Department of Endocrinology, Shandong Provincial Hospital Affiliated to Shandong First Medical University, Jinan, 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