Coexistence of endometriosis and thyroid autoimmunity in infertile women: impact on in-vitro fertilization and reproductive outcomes

Objective: To evaluate the prevalence and impact of impaired thyroid-stimulating hormone (TSH) levels on the reproductive outcomes of in vitro fertilization patients diagnosed with endometriosis and compared to controls without endometriosis. Design: Retrospective cohort study on prospectively collected data Setting: Tertiary care University Hospital Participants: Infertile women with histopathological diagnosis of endometriosis. Methods: for 12 months (January 2018 to January 2019), women were deemed suitable and subsequently divided according to serum thyroid-stimulating hormone levels above or below 2.5 mIU/L and compared to patients without endometriosis. Needed sample size was at least 41 patients for each cohort of women. Co-primary outcomes were the live birth rate (LBR), clinical pregnancy rate (CPR) and pregnancy loss rate (PLR). Results: 226 women (45 with endometriosis and 181 controls without endometriosis) were included. Diagnoses of Hashimoto thyroiditis were significantly more frequent in women with rather than without endometriosis (14/45 (31.1%) vs 27/181 (14.9%); p=0.012). Similarly, in women with endometriosis, Hashimoto diagnosis rates were higher with TSH ≥2.5 mIU/L compared to TSH <2.5 mIU/L (9/15 (60%) vs 5/30 (16.6%); p=0.001), so were the Hashimoto diagnosis rates in control group (women without endometriosis) with TSH ≥2.5 mIU/L compared to TSH <2.5 mIU/L (17/48 (35.4%) vs 10/133 (7.5%), respectively; p=0.001). Effect size analysis confirmed an increased risk of Hashimoto thyroiditis in women with endometriosis and TSH ≥2.5 mIU/L compared to women with endometriosis and TSH <2.5 mIU/L ((risk ratio (RR) 3.60 (95% CI 1.46 to 8.86)) and in women with endometriosis and TSH ≥2.5 mIU/L compared to non-endometriotic euthyroid patients (RR 7.98 (95% CI 3.86 to 16.48)). Dysmenorrhea risk was higher in endometriotic euthyroid women compared to euthyroid patients with no endometriosis (RR 1.87 (95% CI 1.21 to 2.87)). The risk was still increased in euthyroid women with endometriosis relative to dysthyroid women with no endometriosis (RR 1.97 (95% CI 1.11 to 3.50)). There were no significant differences between the four groups for CPR, LBR, PLR and retrieved oocytes, immature oocytes, degenerated and unfertilized oocytes, cultured blastocysts, embryos and transferred embryos. Limitations: Retrospective design, limited sample size and use of different ovarian stimulation protocol. Conclusions: Thyroid autoimmunity seems more common in women with endometriosis and thyroid-stimulating hormone over 2.5 mIU/L. However, there was no significant impact on in vitro fertilization and reproductive outcomes related to the coexistence of endometriosis, Hashimoto disease and higher thyroid-stimulating hormone levels. Due to limitations of the study, additional evidence is required to validate the abovementioned findings.