ODP429 Treatment of high-normal TSH levels in women with unexplained infertility is associated with an increased conception rate
Authors: Galbiati Francesca , Jokar Tahereh O , Howell Lars M , Fourman Lindsay T , Fazeli Pouneh 
Published: November 2022

Unexplained infertility (UI), defined as the inability to conceive after 12 months of unprotected intercourse with no identified cause, affects up to 30% of infertile couples. Women with UI are significantly more likely to have a TSH level in the high-normal range (TSH between 2.5-5 mIU/L) as compared to a control population of women with infertility secondary to a partner with severe oligospermia. It is not known whether treating high-normal TSH levels with levothyroxine results in a higher rate of conception. We performed a cross-sectional study at a large academic health system in women with infertility and TSH levels between 2.5-5 mIU/L to compare rates of conception in women who were treated with levothyroxine versus those who were not treated with levothyroxine. We hypothesized that treatment with levothyroxine would result in a higher conception rate. We identified 126 women who presented for evaluation of infertility between 1/1/2000-6/30/2017 who met our inclusion criteria of a TSH in the high-normal range (2.5 mIU/L &lt; TSH &lt; 5 mIU/L) and either UI (80%, n=101) or infertility due to a severely oligospermic (semen concentration &lt;1 million/mL) partner (20%, n=25). All subjects (n=126) had a normal prolactin level (&lt; 20 ng/mL), regular menstrual cycles every 21-35 days with &lt;5 days of inter-cycle variability, a day 3 follicle stimulating hormone (FSH)&lt; 10 and no other identified cause of infertility. Male partners of women with unexplained infertility had a semen concentration of &gt;15 million/mL, motility &gt;40% and morphology &gt;4% based on 2010 WHO criteria. Thirty-one percent (n=39) were treated with levothyroxine (LT+) by their primary providers, whereas 69% (n=87) were not treated with levothyroxine (LT-). Women treated with levothyroxine were older than those not treated (mean + SD, LT+: 32.5 + 2.4 years vs LT-: 31. 0 + 3. 0 years, p=0. 005) but were of similar BMI (median (interquartile range), LT+: 24.1 [21.7, 28.3] kg/m2 vs LT-: 23.6 [20.9, 27. 0] kg/m2, p=0.38). Baseline TSH was significantly higher in the group treated with levothyroxine (3.55 [3. 07, 4.19] mIU/L compared to the untreated group (2.93 [2.66, 3.40] mIU/L, p&lt; 0. 0001). In women for whom follow-up data was available (n=105), a significantly higher percentage of women treated with levothyroxine (100%) achieved pregnancy compared to those not treated with levothyroxine (92%, p value 0. 027) and this was also true when only evaluating women with UI (n=86) (LT+: 100% versus LT-: 89.5%, p=0. 02). There was no significant difference in time to conception between the two groups (p=0.85). Women with high normal TSH levels (TSH between 2.5-5 mIU/L) treated with levothyroxine had a higher rate of conception compared to those not treated. Prospective, randomized studies are needed to determine whether treatment with levothyroxine could improve conception rates in patients with high-normal TSH levels.

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