Relationship between hypothyroidism and gestational diabetes mellitus: a retrospective cohort study

Background: Approximately 2-10% of pregnant women experience subclinical hypothyroidism during pregnancy. Although some studies have shown that primary hypothyroidism increases the risk of gestational diabetes mellitus (GDM), there are contradictory results. Hence, this study aimed to determine the relationship between hypothyroidism and GDM. Methods: This is a retrospective cohort study in which the researchers followed up 340 pregnant women (170 with hypothyroidism as exposed group and 170 without hypothyroidism as unexposed group) for GDM. To analyse the data, chi-square, Fisher's exact test and independent t-test were employed. Results: The incidence of GDM in the hypothyroidism group was higher than that of the group without hypothyroidism (11.8% vs. 10.6%, p = 0.731). Moreover, the risk of GDM (95% CI:0.61; 2.02) was 1.11 times higher among women with hypothyroidism. However, the observed association was not statistically significant. The mean two-hour oral glucose tolerance test (OGTT) level in pregnant women with hypothyroidism (108.94 +/- 19.89 mg/dl) was significantly higher than in the other group (104.49 +/- 18.43 mg/dl) with a p-value of 0.033. Conclusions: This study displayed that the risk of GDM is 11% higher among women with hypothyroidism. Furthermore, the difference in the mean two-hour OGTT level in pregnant women with hypothyroidism was 4.4 mg/dl higher than in the other group.