Plain language summary
Thyroid hormones play a vital role in regulating metabolism. Adequate thyroid hormone levels are also critical during pregnancy for optimal fetal growth and development. The foetus is dependent on maternal thyroid hormones until its own thyroid gland matured in the second half of pregnancy. Furthermore, pregnancy impacts thyroid function leading to an increased demand for thyroid hormones. Thyroid disease has been associated with Vitamin D deficiency. During pregnancy, both thyroid disorders and Vitamin D deficiency can have adverse effects on pregnancy and pregnancy outcomes, hence a potential link between Vitamin D status and thyroid function has been postulated. To fill the gaps in previous research, this retrospective cohort study aimed to explore the associations between Vitamin D status and thyroid function throughout the pregnancy, in each trimester. The analysis of hospital data collected in Beijing demonstrated an association between Vitamin D levels and thyroid function throughout pregnancy. Such interlink appeared to be dynamic and changed depending on the stage of pregnancy. The author's findings affirmed that maintenance of adequate Vitamin D levels supports normal thyroid function which is an important nutritional strategy for a healthy pregnancy.
Abstract
Optimal Vitamin D (VitD) status and thyroid function are essential for pregnant women. This study aimed to explore associations between dynamic VitD status and thyroid function parameters in each trimester and throughout the pregnancy period. Information on all 8828 eligible participants was extracted from the Peking University Retrospective Birth Cohort in Tongzhou. Dynamic VitD status was represented as a combination of deficiency/sufficiency in the first and second trimesters. Thyroid function was assessed in three trimesters. The associations between VitD and thyroid function were assessed by multiple linear regression and generalized estimating equation models in each trimester and throughout the pregnancy period, respectively. The results indicated that both free thyroxine (fT4; β = 0.004; 95%CI: 0.003, 0.006; p < 0.001) and free triiodothyronine (fT3; β = 0.009; 95%CI: 0.004, 0.015; p = 0.001) had positive associations with VitD status in the first trimester. A VitD status that was sufficient in the first trimester and deficient in the second trimester had a lower TSH (β = -0.370; 95%CI: -0.710, -0.031; p = 0.033) compared with the group with sufficient VitD for both first and second trimesters. In conclusion, the associations between VitD and thyroid parameters existed throughout the pregnancy. Maintaining an adequate concentration of VitD is critical to support optimal thyroid function during pregnancy.
Methodological quality
Jadad score
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Not applicable
Allocation concealment
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