Subclinical hypothyroidism in infertile women: the importance of continuous monitoring and the role of the thyrotropin-releasing hormone stimulation test.

The aim of our study was to assess the prevalence of subclinical hypothyroidism (SH) after administering a thyrotropin-releasing hormone (TRH) stimulation test among women with normal serum thyroid-stimulating hormone (TSH) levels and various causes of infertility. Eighty-seven infertile women (39 with ovulation disorders and 48 with other causes of infertility) had a TRH stimulation test on day 3 - 7 of their cycle. Exaggerated TSH response (>30 mIU/l at 20, 40 or 60 min) following intravenous injection of 400 microg TRH was defined as SH. The TRH test was performed 2 - 4 months after the first visit to the clinic. We found that the prevalence of SH was significantly higher among women with ovulation disorders (20.5%) than among women with normal ovulation (8.3%). In addition, we found that although basal TSH levels were normal at recruitment, 2 - 4 months later these levels were abnormally high in 8% of the women. All these women had an abnormal TRH test. We recommend performing TRH stimulation testing in women suffering from ovulation disorders who have normal basal TSH levels, followed by repeat assessments of thyroid function to enable treatment with thyroxine in cases with abnormal results.