Delaying Thyroxine Until Positive Beta-Human Chorionic Gonadotropin is Safe for Patients Receiving Fertility Therapy: Applying New ATA Guidelines to Subclinical Hypothyroidism.

Abstract

This study sought to examine the effect of changing TSH threshold recommendations from 2.5 to 4 mIU/L before fertility therapy on the prevalence of early gestational subclinical hypothyroidism (SCH) (TSH2 >2.5 mIU/L) and to evaluate implications on progression to clinical pregnancy (defined as detection of cardiac activity on ultrasound). A retrospective chart review was performed in an academic fertility clinic on all patients with a measured pre-treatment TSH (TSH1) and positive beta-human chorionic gonadotropin following fertility treatment. The study assessed the effect of TSH2 on ongoing pregnancy, both in patients newly diagnosed with SCH and in patients previously receiving LT4, stratified by initial TSH. Of 482 women included in the study, baseline TSH (TSH1) was <2.5 mIU/L in 333 women (69%) and 2.5-4 mIU/L in 64 women (13.2%). Eighty-five women were taking LT4 at baseline (17.6%). Among women with a TSH1 between 2.5 and 4 mIU/L, the corresponding TSH in early pregnancy (TSH2) was <2.5 mIU/L in 35 women (55%). Overall, there was no difference in progression to clinical pregnancy between women with a TSH2 of 2.5-4 mIU/L compared with women with a TSH2 <2.5 mIU/L (OR 0.70; 95% CI 0.44-1.09). Similarly, when excluding women taking LT4 at baseline, there was no difference in progression to clinical pregnancy (OR 0.90; 95% CI 0.28-2.86). Rate of progression to clinical pregnancy was equivalent between women with an early pregnancy TSH (TSH2) <2.5 and women with a TSH2 of 2.5-4.0 mIU/L. Our findings support initiating LT4 in early pregnancy, as opposed to pre-pregnancy if the TSH remains above cut-off because there does not appear to be a difference in in early pregnancy outcomes if treatment is delayed.