Objective: To investigate the prevalence of subclinical hypothyroidism (SH) diagnosed by thyrotropin-releasing hormone (TRH) stimulating test in infertile women with basal thyroid-stimulating hormone (TSH) levels of 2.5 to 5.0 mIU/L.
Methods: This study was performed in 39 infertile women with ovulatory disorders (group 1) and 27 infertile women with male infertility only (group 2, controls) who had basal serum TSH levels of 2.5 to 5.0 mIU/L and a TRH stimulating test. Serum TSH levels were measured before TRH injection (TSH0) and also measured at 20 minutes (TSH1) and 40 minutes (TSH2) following intravenous injection of 400 µg TRH. Exaggerated TSH response above 30 mIU/L following TRH injection was diagnosed as SH. Group 1 was composed of poor responders (subgroup A), patients with polycystic ovary syndrome (subgroup B) and patients with WHO group II anovulation except poor responder or polycystic ovary syndrome (subgroup C).
Results: The prevalence of SH was significantly higher in group 1 of 46.2% (18/39) compared with 7.4% (2/27) in group 2 (P=0.001). TSH0, TSH1, and TSH2 levels were significantly higher in group 1 than the corresponding values in group 2 (P<0.001, P<0.001, P<0.001). In group 1, TSH1 and TSH2 levels were significantly lower in subgroup C compared with those in subgroup A and B (P=0.008, P=0.006, respectively).
Conclusion: TRH stimulation test had better be performed in infertile women with ovulatory disorders who have TSH levels between 2.5 and 5.0 mIU/L for early detection and appropriate treatment of SH.
Keywords: Infertility; Ovulatory disorder; Subclinical hypothyroidism; Thyrotropin-releasing hormone stimulating test.