Levothyroxine for a high-normal TSH in unexplained infertility

Unexplained infertility affects nearly one-third of infertile couples. Women with unexplained infertility are more likely to have a high-normal thyroid-stimulating hormone level (TSH: 2.5-5 mIU/L) compared to women with severe male factor infertility. Practice guidelines vary on whether treatment should be initiated for TSH levels >2.5 mIU/L in women attempting conception because the effects of treating a high-normal TSH level with levothyroxine are not known. We evaluated conception and live birth rates in women with unexplained infertility and high-normal TSH levels.

Retrospective study including 96 women evaluated for unexplained infertility at a large academic medical centre between 1 January 2000 and 30 June 2017 with high-normal TSH (TSH: 2.5-5 mIU/L and within the normal range of the assay) who were prescribed (n = 31) or not prescribed (n = 65) levothyroxine. Conception and live birth rates were assessed.

The conception rate in the levothyroxine group was 100% compared to 90% in the untreated group (p = .086 unadjusted; p < .05 adjusted for age; p = .370 adjusted for TSH; p = .287 adjusted for age and TSH). The live birth rate was lower in the levothyroxine group (63%) compared to the untreated group (84%) (p = .05 unadjusted; p = .094 adjusted for age; p = .035 adjusted for TSH; p = .057 adjusted for age and TSH).

Women with unexplained infertility and high-normal TSH levels treated with levothyroxine had a higher rate of conception but lower live birth rate compared to untreated women, with the limitation of a small sample size. These findings assert the need for prospective, randomized studies to determine whether treatment with levothyroxine in women with unexplained infertility and high-normal TSH is beneficial.