Research Article Correlation between Maternal Vitamin D and Thyroid Function in Pregnancy with Maternal and Neonatal Outcomes: A Cross-Sectional Study Salma Ahi , 1 Mohsen Adelpour, 1 Iman Fereydooni, 2 and Naser Hatami 2 1 Research Center for Noncommunicable Diseases, Jahrom University of Medical Sciences, Jahrom, Iran 2 Student Research Committee, Jahrom University of Medical Sciences, Jahrom, Iran Correspondence should be addressed to Salma Ahi; salmaahi.61@gmail.com Received 24 August 2021; Revised 2 January 2022; Accepted 6 January 2022; Published 29 January 2022 Academic Editor: Flavia Prodam Copyright © 2022 Salma Ahi et al. is is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Background. e aim of this study was to evaluate the prevalence of vitamin D deficiency in pregnant women to investigate the relationship between vitamin D level and thyroid function. Methods. In this cross-sectional descriptive study, a total number of 66 patients during the three trimesters of pregnancy were investigated; 22 pregnant women were studied in each trimester of pregnancy. We evaluated thyroid function tests and thyroid autoantibodies (TPOAb and TGAb), as well as the serum level of 25OHD, to determine the relationship between vitamin D level and autoimmune or non-autoimmune thyroid disease in pregnancy. Results. Pearson’s correlation in all subjects showed that vitamin D levels did not have a significant relationship with maternal age. Only in the third trimester, there was a significant difference in maternal age based on their vitamin D status. ere was no significant difference between the trimesters of pregnancy and vitamin D status (P > 0.05). Also, there were no significant differences between serum levels of vitamin D within three trimesters. Examination of thyroid function tests during pregnancy in relation to vitamin D showed that there was no significant Spearman’s correlation between thyroid function status and serum vitamin D level (P > 0.05). ere was no significant difference in the mean level of serum 25OH vitamin D in each subgroup of thyroid status (P > 0.05). Regarding the pregnancy outcomes, two newborns were admitted to NICU, meconium aspiration was in one case, and IUFD in another case led to pregnancy termination. ese four cases were related to the maternal history of hypothyroidism. Conclusion. ere was no significant relationship between vitamin D and pregnancy trimester. e serum level of vitamin D had no particular effect on the outcome of pregnancy and the thyroid gland function. 1. Background Hormonal and multiple metabolic changes during preg- nancy lead to complex effects on the maternal thyroid function [1]. Pregnancy increases stimulation and synthesis of steroid hormones, and it also increases the thyroxine- binding globulin’s (TBG) degradation, TBG levels, total T3, and total T4. Studies have shown that TBG levels double in the 16th–20th week of pregnancy [1]. e level of thyroxin (T4) and triiodothyronine (T3) is regulated by TSH secreted from the pituitary [2, 3]. A large percentage of thyroid hormones in the bloodstream (more than 99%) are bound to the carrier proteins. Most of the thyroid hormones are transmitted by TBG and a lesser extent by transthyretin and albumin. Binding with these proteins prevents the hormone from entering the cell and provides its effect. [4]. So, thyroid disease is the second most common endocrine disorder affecting women of childbearing age [5, 6]. Recently, the evaluations of thyroid function showed that thyroid function tests interpretation depends on the stage of pregnancy [7]. Multiple hormonal and metabolic changes during each pregnancy trimester lead to complex effects on the mother’s thyroid function [8]. ere is a high prevalence of thyroid diseases in women of reproductive age, including chronic Hindawi International Journal of Endocrinology Volume 2022, Article ID 6295775, 7 pages https://doi.org/10.1155/2022/6295775