Is the link between elevated TSH and gestational diabetes mellitus dependant on diagnostic criteria and thyroid antibody status: a systematic review and meta-analysis

Abstract

Purpose: Clinical studies have investigated the prevalence of gestational diabetes mellitus (GDM) in women with subclinical hypothyroidism (SCH). While some studies demonstrate a clear association, others do not. It is possible this may be due to varied diagnostic criteria for SCH and the presence of thyroid antibodies (TA). We conducted a meta-analysis, separating patients diagnosed with SCH using a diagnostic cut-off <4.0 mIU/L from those diagnosed using a cut-off >4.0 mIU/L and determined the association with GDM and factored TA status into our analysis.

Methods: A computerised search of five databases including PubMed, Embase, Cochrane Library, Web of Science and CINAHL returned 787 records. Two independent reviewers assessed abstracts and full texts against pre-specified inclusion and exclusion criteria. Ten cohort studies were included in the final analysis. The diagnostic criteria for SCH and incidence of GDM were extracted from each study. Study quality and risk of bias was assessed by two reviewers.

Results: TSH levels <4.0 mIU/L for SCH diagnosis was not associated with GDM unless patients were TA positive. Studies that used a diagnostic cut-off >4.0 mIU/L saw a significant increase in the odds of GDM, regardless of TA status (OR = 1.60, 95% CI 1.33-1.93).

Conclusions: Women with TSH levels >4.0 mIU/L have an increased odds of GDM regardless of TA status but at TSH levels <4.0 mIU/L, GDM is dependent on TA status. The use of TSH levels to identify pregnancies at risk of GDM is a novel concept that warrants exploration.

Keywords: Diagnostic criteria; GDM; Subclincial hypothyroidism; Thyroid antibody.