Impact of hormone replacement therapy on serum thyroid-stimulating hormone: a retrospective analysis.

RESEARCH QUESTION: What is the impact of hormone replacement therapy (HRT) on serum thyroid-stimulating hormone (TSH) during endometrial preparation for single-embryo transfer (SET)?

DESIGN

This retrospective cohort study included 516 women (≤49 years) who underwent SET with either autologous or donor oocytes, between January 2022 and January 2023 at IVI Rome. TSH was measured at baseline (T0), during endometrial thickness assessment (T1), on embryo transfer day (T2), and at the pregnancy test (T3). TSH >2.5 mU/l was treated with levothyroxine. HRT consisted of oral estradiol valerate (6 mg/day) followed by vaginal progesterone (800 mg/day).

RESULTS

TSH significantly increased at T1 and T3 compared to T0 (TSH0 1.67 mU/l, 95%CI 1.59-1.74; TSH1 1.93 mU/l, 95%CI 1.83-2.04, p < 0.001; TSH3 2.08 mU/l, 95%CI 1.97-2.18, p < 0.001). Univariate analysis showed that patients with a TSH < 2.5 mU/l at T3 had higher miscarriage rate (15.2%, 95%CI 10.8-20.6 vs 29.7%, 95%CI 19.7-41.4; p = 0.01) and lower ongoing pregnancy (65.8%, 95%CI 60-71.3 vs 49.5%, 95%CI 39.5-59.5; p = 0.005) and live birth rates (62.5%, 95%CI 56.3-68.3 vs 47.5%, 95%CI 37.3-57.8; p = 0.01). Multivariate analysis showed no significant association between TSH >2.5 mU/l and pregnancy (aOR 0.64, 95%CI 0.36-1.14, p=0.13) or miscarriage (aOR 1.78, 95%CI 0.87-3.66, p = 0.11), while negative association was observed between TSH >2.5 mU/l and live birth (aOR 0.54, 95%CI 0.32-0.92, p = 0.02).

CONCLUSIONS

HRT significantly increased TSH concentrations. Additionally, a TSH >2.5 mU/l did not correlate with miscarriage, but it was significantly associated with lower live birth rates. Further studies are needed to clarify HRT's impact on thyroid function and reproductive outcomes.