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Association between age-specific preconception thyroid-stimulating hormone (TSH) and birth weight: a retrospective
Xi Bai1, Zhibo Zhou2, Xiaonan Guo3
1Key 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, China.
BMJ Open
|January 7, 2026
Summary
Young women (20-24 years) with abnormal preconception thyroid-stimulating hormone (TSH) levels face increased risks of delivering large for gestational age (LGA) babies. Thyroid function is crucial for fetal birth weight, especially in younger maternal age groups.
Area of Science:
- Reproductive endocrinology
- Maternal-fetal medicine
- Thyroidology
Background:
- Maternal thyroid function significantly influences fetal development, particularly birth weight.
- Age is a key regulator of thyroid function, necessitating age-specific considerations.
- Understanding preconception thyroid health is vital for optimizing pregnancy outcomes.
Purpose of the Study:
- To investigate the association between age-specific preconception thyroid-stimulating hormone (TSH) levels and fetal birth weight.
- To determine if TSH levels impact the incidence of large for gestational age (LGA), small for gestational age (SGA), and appropriate for gestational age (AGA) infants across different maternal age groups.
Main Methods:
- A large cohort study involving 97,755 Chinese women aged 20-39 years.
- Participants were stratified into four age groups: 20-25, 25-29, 30-34, and 35-39 years.
- Preconception TSH levels (within 6 months prior to pregnancy) and birth weight outcomes (LGA, SGA, AGA) were analyzed using restricted cubic spline and logistic regression models.
Main Results:
- Preconception TSH levels varied significantly across the four maternal age groups.
- In women aged 20-24 years, TSH levels were associated with LGA and AGA outcomes. Specifically, TSH levels between 1.32-2.12 mIU/L were linked to lower odds of LGA and higher odds of AGA.
- No significant associations between age-specific TSH levels and LGA, SGA, or AGA risks were observed in women aged 25-39 years.
Conclusions:
- Preconception TSH levels are significantly associated with LGA and AGA in younger women (20-24 years) but not in older age groups (25-39 years).
- Younger women should monitor their thyroid function preconceptionally, as abnormal TSH levels may increase the risk of delivering LGA infants.
- These findings highlight the importance of age-specific reference ranges and monitoring for preconception thyroid health.
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