Unexplained Infertility Linked to Higher Thyroid-Stimulating Hormone in Women

A physician pointing to a thyroid gland model
A physician pointing to a thyroid gland model
Study raises the question of whether treatment with thyroid hormone replacement for individuals with TSH levels >2.5 mIU/L may be an economical first step in treating unexplained infertility.

Women found to have a thyroid-stimulating hormone (TSH) level of ≥2.5 mlU/L with no known thyroid disease may have a higher risk for unexplained infertility (UI), according to a study published in the Journal of Clinical Endocrinology and Metabolism.

Researchers identified 239 women and divided them into 2 study groups: the UI group (n=187) and the severe male factor infertility group (n=52; azoospermic [n=39] or severely oligospermic [n=13]). The purpose of the study was to determine whether high, yet within normal range, blood levels of TSH or prolactin levels were associated with UI.

It was hypothesized that higher levels of TSH and prolactin levels, despite being in the normal range, were associated with UI when compared with women with a normal infertility evaluation and a partner who was azoospermic/severely oligospermic.

The study results found mean TSH levels to be significantly higher in the UI group when compared with those in the severe male factor group (1.95 mIU/L [interquartile range, 1.54-2.61] and 1.66 mIU/L [interquartile range, 1.25-2.17]; P =.003, respectively).

When results were adjusted for body mass index, age, current history of smoking, and combined past and current history of smoking, TSH levels remained higher for those in the UI group (P <.02, P <.01, P <.01, and P <.01, respectively). Overall, study results found the percentage nearly double for those participants in the UI group with a TSH level ≥2.5 mIU/L compared with those in the severe male factor group (26.9% vs 13.5%; P <.05).

No significant difference in prolactain levels were observed between the 2 groups; however, of those found to have an elevated thyroid peroxidase antibody levels, the mean level was found to be significantly higher in the severe male factor group when compared with the UI group (90.4 IU/mL [interquartile range, 18.4-2994.3] vs 13.3 IU/mL [interquartile range, 10.2-18]; P =.03, respectively.)

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Researchers concluded that a significantly higher TSH level (≥2.5 mIU/L) was found in women with unexplained fertility when compared with a control group of women with a normal fertility evaluation except for an azoospermic/severely oligospermic partner. However, there were no differences observed in prolactain levels between groups.

“[F]uture studies will be necessary to determine if treatment of high-normal TSH levels decreases time to conception in couples with unexplained infertility,” concluded the researchers.

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Orouji Jokar T, Fourman LT, Lee H, Mentzinger K, Fazeli PK. Higher TSH levels within the normal range are associated with unexplained infertility [published online December 19, 2017]. J Clin Endocrinol Metab. doi: 10.1210/jc.2017-02120