[Preclinical hypothyroidism and disorders of ovarian function]

For sensitive assessment of thyroid function a TRH stimulation test using 200 micrograms TRH i.v. was routinely performed in 304 women admitted for evaluation and treatment of infertility. In 37 cases (12.2%) the reaction of TSH 30 min after injection of TRH i.v. was enhanced (by definition of a peak TSH level greater than 25 mIU/l), according to mild or subclinical hypothyroidism. Approximately 14 (14/37 = 37.8%) of these patients were found to have slightly elevated serum PRL values (mean PRL greater than 15 ng/ml). Cycle analysis by means of basal body temperature and evaluation of progesterone and oestradiol values, supplied evidence of luteal phase deficiency in 8 and anovulation in 3 cases. Another group of 11 patients with hypothyroidism involved oligo-/amenorrhoea, hirsutism and hyperandrogenaemia. After treatment with 50-150 micrograms l-thyroxine daily for at least 4 to 6 weeks, elevated PRL values significantly decreased (mean level less than 15 ng/ml, p less than 0.01) in 9 out of 12 patients and testosterone levels slightly decreased in 5 out of 8 patients. An improvement of the cyclical ovarian function could be observed by the significant increase of the average progesterone concentration in the luteal phase. During therapy with l-thyroxine, 4 pregnancies occurred. From these results we conclude, that mild hypothyroidism may cause ovarian insufficiency. Assessment of thyroid function should be mandatory in infertile patients with elevated prolactin levels or chronic anovulation.