Associations between thyroid function and autoimmunity indicators and in vitro fertilization/intracytoplasmic sperm injection outcomes in euthyroid PCOS women

To the Editor: Polycystic ovary syndrome (PCOS), characterized by oligo-anovulation, hyperandrogenism, and polycystic ovaries, is the most common endocrinopathy affecting 5–15% of women of reproductive age.[1,2] It can result in a wide range of endocrine and metabolic disorders, including anovulatory infertility, insulin resistance, impaired glucose tolerance, diabetes, obesity, dyslipidemia, and cardiovascular disease, which can occur in different combinations and with different intensities.[2] Thyroid dysfunction is another common endocrine disorder associated with ovarian dysfunction, menstrual irregularities, subfertility, and infertility in women of reproductive age. The most prevalent cause of thyroid dysfunction is autoimmune thyroid disease (AITD), which is very frequent in infertile women and associated with adverse assisted reproduction technology (ART) outcomes.[3] Considering the high prevalence of AITD and PCOS in reproductive-age women, the common etiology and pathogenesis have been elucidated, including the polymorphisms of susceptibility genes, thymus disorders, vitamin D deficiency, and sex hormone dysregulation.[4] Several studies have elucidated the negative association between thyroid function and autoimmunity indicators and in vitro fertilization/intracytoplasmic sperm injection (IVF/ICSI) outcomes and pregnancy outcomes.[3] However, there is still a lack of evidence on the associations between thyroid function and autoimmunity indicators and IVF/ICSI outcomes among PCOS women. We aim to investigate the potential effects of thyroid function and autoimmunity indicators on IVF/ICSI early development and pregnancy outcomes among euthyroid PCOS women. The study was approved by the Institutional Review Board of Peking University Third Hospital (No. 2021SZ-011). Written informed consent was obtained from all participants included in the study. We initially retrospectively included 1801 PCOS women aged between 20 years and 45 years undergoing their first fresh IVF/ICSI cycles with autologous oocytes at the Center for Reproductive Medicine of Peking University Third Hospital from January 1, 2018, to December 30, 2020. According to the Rotterdam criteria, PCOS is diagnosed by at least two of the three symptoms: oligo- or anovulation (oligo- or amenorrhea), hyperandrogenism (clinical or biochemical), and/or polycystic ovary morphology.[1] The exclusion criteria were as follows: (1) history of hyperthyroidism, hypothyroidism, thyroid neoplasms, thyroid hormone/antithyroid medication, or thyroid surgery (n = 15); (2) history of recurrent spontaneous abortion (n = 2); (3) history of congenital adrenal hyperplasia, hyperprolactinemia, Cushing's syndrome, or androgen-secreting tumors (n = 1); (4) chromosomal abnormalities in either of the spouses (n = 19); (5) in vitro maturation (IVM) cycles or preimplantation genetic testing (PGT) cycles (n = 27); and (6) missing information and other important medical conditions that may affect IVF outcomes (i.e., endometriosis, severe oligospermia) (n = 187). Finally, a total of 1550 women were involved in the present study. All enrolled patients received standardized and individualized IVF protocols. Details on ovarian stimulation, oocyte retrieval, insemination technique, embryo culture, and embryo transfer have been previously described.[5] Data were extracted from electronic medical records. Serum total thyroxin (T4), free thyroxin (FT4), TSH, thyroid peroxidase antibody (TPOAb), and thyroglobulin antibody (TGAb) levels were determined by a fully automatic chemiluminescence immunoassay analyzer (ADVIA Centaur XP, Siemens Healthcare Diagnostics, Germany) within six months before the initiation of ovarian stimulation. All lab technicians were blinded to other information about the participants. Positive TPOAb and TGAb were defined as >60 U/mL in concentrations according to the manufactory's instructions. The definition of the study outcomes, including normal fertilization, high-quality embryos, implantation, clinical pregnancy, and live birth, have been previously described.[6] Deliveries of multiple pregnancies were counted as one live birth. The baseline reproductive and cycle characteristics were described using median (interquartile range [IQR]) or n (%). Thyroid function and autoimmunity indicator levels were transformed by natural logarithm due to right skewness and categorized into tertiles. Multivariate generalized linear models were conducted to analyze the effects of thyroid function and autoimmunity indicators on IVF/ICSI early development and pregnancy outcomes. A Poisson distribution and log link function were specified for retrieved oocyte count, MII oocyte count, normal fertilized embryo count, normal cleavage embryo count, high-quality embryo count, and blastocyst formation count; a binomial distribution and logit link function were specified for implantation, clinical pregnancy, and live birth. To better interpret the results, we calculated the percentage change and associated 95% CI as follows: [exp (β) – 1] × 100. Tests for linear trends were conducted using an ordinal number (1, 2, and 3) for each tertile of thyroid function and autoimmunity indicators. We retained the potential covariates in the final models when they led to >10% changes in the effect estimates.[7] All models were adjusted for the same set of covariates for consistency. Data were further stratified by BMI (<30 kg/m2vs. ≥30 kg/m2), age (<35 years vs. ≥35 years), and androgen level (normal vs. hyperandrogenism) to evaluate the possible modification effect of obesity and age. Multivariate generalized additive models (GAMs) were used to analyze the potential non-linear effects. Sensitivity analyses were conducted by: (1) restricting the analyses to women applying a GnRH antagonist protocol for ovulation stimulation; and (2) restricting the analyses to women with a primary infertility diagnosis. Statistical analyses were performed with R (R version 4.0.3, R Foundation, Vienna, Austria). GAM was conducted using the R package "mgcv" (version 1.8-40). P-values of <0.05 was considered statistically significant. The baseline reproductive and cycle characteristics of the study population are listed in Supplementary Table 1, https://links.lww.com/CM9/B918. Women in the positive thyroid autoimmunity (TAI) group had less AFC, retrieved oocyte count, MII oocyte count, normal fertilization count, and normal cleavage count (all P <0.05) and higher serum T4, FT4, TSH, TGAb, and TPOAb levels (all P <0.01). No other characteristics differed significantly across positive and negative TAI groups. As shown in Supplementary Table 2, https://links.lww.com/CM9/B918, declining trends were observed in the six early development outcomes when considering TGAb levels in PCOS women (all Ptrend <0.05). Compared with PCOS women in the T1 of TGAb, women in the T3 had significant declines in retrieved oocyte count (adjusted percent change of −4.72; 95% CI: −8.09, −1.23), MII oocyte count (adjusted percent change of −4.78; 95% CI: −8.24, −1.19), normal fertilized embryo count (adjusted percent change of −8.10; 95% CI: −12.22, −3.81), normal cleavage embryo count (adjusted percent change of −8.03; 95% CI: −12.17, −3.71), high-quality embryo count (adjusted percent change of −6.46; 95% CI: −11.29, −1.38), and blastocyst formation count (adjusted percent change of −11.58; 95% CI: −20.24, −2.07), respectively. Similarly, blastocyst formation count was statistically significantly declined (adjusted percent change of −11.78; 95% CI: −20.53, −2.15) for PCOS women in the T3 of TPOAb in comparison with those in the T1, with significant declining trends (Ptrend = 0.02). These associations remained largely unchanged when these thyroid function and autoimmunity indicators were modeled as continuous variables. Besides, we observed that continuous variables rather than tertiles of TPOAb were associated with decreased retrieved oocyte count, MII oocyte count, normal fertilized embryo count, and normal cleavage embryo count (all P <0.05). There was no significant association between thyroid function and autoimmunity indicators and pregnancy outcomes in PCOS women [Supplementary Table 3, https://links.lww.com/CM9/B918]. The results of analyses focused on TAI indicators classified by clinical reference value are listed in Supplementary Table 4, https://links.lww.com/CM9/B918. Stratified analyses were further performed to explore the potential interaction effect. We found obesity-, age-, and androgen-specific negative associations between TAI and IVF/ICSI early development outcomes [Supplementary Tables 5–7, https://links.lww.com/CM9/B918]. The results of GAMs are listed in Supplementary Figures 1 and 2, https://links.lww.com/CM9/B918. Two sensitivity analyses confirmed the robustness of the results [Supplementary Tables 8–11, https://links.lww.com/CM9/B918]. We found significant adverse effects of TAI indicators on IVF/ICSI early development outcomes but not pregnancy outcomes, suggesting the adverse effect of TAI on oogenesis and early embryogenesis in PCOS women. So far, scarce studies have reported the impact of thyroid dysfunction and/or TAI on oocyte maturation, fertilization, and embryo quality in PCOS women.[8,9] Our findings provide supporting evidence for research in this field. Many studies have explored the mechanism of impaired oogenesis and embryogenesis caused by thyroid dysfunction and/or TAI, including autoimmune activity and cytotoxic reactions.[10] Moreover, since AITD and PCOS have possible common etiology and pathogenesis (i.e., polymorphisms of susceptibility genes, sex hormone dysregulation, and vitamin D deficiency),[4] the negative associations between TAI and IVF/ICSI outcomes may also be related to the sensitivity of PCOS women to immune inflammatory responses and cytotoxicity caused by thyroid autoantibodies. We found that thyroid autoantibodies have more significant effects on IVF/ICSI early development outcomes in obese PCOS women, those aged under 35 years, and those with hyperandrogenism. Therefore, we emphasize the importance of preconception thyroid monitoring in PCOS women, especially in obese, young, and hyperandrogenic PCOS women. This present study has several limitations. First, we cannot rule out bias in retrospective data collection due to its retrospective nature. Second, residual confounding may influence our findings. Third, we did not consider possible changes in thyroid function during pregnancy. Lastly, we did not consider the use of levothyroxine on account of the retrospective design, whereas our previous randomized clinical trial has shown no effect of levothyroxine on IVF/ICSI outcomes.[5] In conclusion, in the present study, our findings support the impact of TAI on oogenesis and early embryogenesis in PCOS women. These results were more significant in obese, young, and hyperandrogenic PCOS women. Although further experimental and more large-scale multicenter prospective studies will help to confirm our findings, we emphasize that PCOS women must attach importance to preconception thyroid testing and management.