Meta-analysis of the association between maternal subclinical hypothyroidism and gestational diabetes mellitus

Background: Subclinical hypothyroidism (SCH) and gestational diabetes mellitus (GDM) are common endocrine disorders that occur during pregnancy.

Objective: To determine whether the risk of GDM differs between pregnant women with normal thyroid function and those with SCH.

Search strategy: MEDLINE, EMBASE, the Cochrane Library, and Web of Science were searched for studies published in English from inception to March 1, 2017, using combinations of the search terms "thyroid dysfunction", "thyroid diseases", "subclinical hypothyroidism", "hypothyroxinemia", "thyrotropin", "gestational diabetes", "hyperglycemia in pregnancy", and "adverse pregnancy outcomes".

Selection criteria: We selected cohort studies that included pregnant women with SCH; in which the outcome of interest was, or included, the incidence of GDM; and that had data available for both the SCH and GDM groups. Studies were excluded if assisted reproductive technologies were used to achieve pregnancy; reviews, abstracts, and case reports were also excluded.

Data collection and analysis: Eleven studies were included in the analysis. Summary odds ratios (ORs) for the risk of GDM were calculated.

Main results: SCH with positive antithyroid autoantibodies markedly increased GDM risk (OR 3.22, 95% confidence interval 1.72-6.03, I² =55%).

Conclusion: SCH with positive antithyroid autoantibodies in pregnancy is associated with an increased risk of GDM.