Gestational diabetes incidence in women with subclinical hypothyroidism and euthyroid women

Introduction: The association between subclinical hypothyroidism (SCH) and gestational diabetes (GDM) is controversial. This study was performed with aim to compare the incidence of GDM in women with SCH and euthyroid women. Methods: In this prospective study, data obtained from 1026 pregnant women (including 683 cases of euthyroid and 343 women with SCH) participating in the cohort study of Tehran thyroid and pregnancy (TTP) was used. Serum levels of thyrotropin (TSH), thyroxine (T4), T3-uptake, and thyroid peroxidase antibody (TPOAb) were measured at first visit of the first trimester of pregnancy; based on this, euthyroid and SCH women were identified. These two groups were evaluated for gestational diabetes. Data were analyzed using STATA software (version 13). The continuous variables were compared between the two groups using independent t-test and Mann-Whitney test, and categorical variables using chi-square test or Fisher's exact test. Log-binomial model was used to identify the effect of SCH and levothyroxine on GDM. P< 0.05 was considered statistically significant Results: There was no significant difference in the incidence of GDM in SCH women compared to the control group either in the unadjusted model or after adjusting for the effective risk factors. Also, there was no significant difference in the incidence of GDM between SCH with TPOAb+, SCH with TPOAb-, and euthyroid groups. The risk of GDM in the TPOAb positive group was not significantly different from TPOAb negative group. Serum TSH (p=0.9), T4 (p=0.8), T3-uptake (p=0.7), and TPOAb (p=0.4) levels were not significantly different between the GDM and non-GDM groups. Conclusion: Although no significant association was found between GDM and SCH in this study, however, it seems that due to various factors affecting the incidence of SCH and GDM, such as different diagnostic criteria and reference values, proving this issue requires further studies.