Thyroid autoimmunity not linked to embryo quality, birth rate with assisted reproduction
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Key takeaways :
- No differences were seen in embryo quality or live birth rate for women with vs. without thyroid autoimmunity undergoing assisted reproduction.
- Clinical pregnancy and early pregnancy loss rates were similar.
Thyroid autoimmunity among women with infertility was not associated with embryo quality or cumulative live birth rate after IVF or intracytoplasmic sperm injection, researchers reported in Thyroid.
“Associations between thyroid autoimmunity and pregnancy outcomes have long been investigated, and several meta-analyses have shown increased risks of pregnancy loss and preterm birth in women with thyroid autoimmunity,” Meng V. Rao, MD, from the department of reproduction and genetics at First Affiliated Hospital of Kunming Medical University, China, and colleagues wrote in study background. “However, recently published population-based studies have not supported any detrimental effects of thyroid autoimmunity on pregnancy outcomes following assisted reproductive technology.”
Rao and colleagues aimed to evaluate any associations between maternal thyroid autoimmunity and embryo development among women with infertility undergoing assisted reproduction. In a retrospective cohort study, they enrolled 499 thyroid autoimmunity-positive (mean age, 31.6 years) and 2,945 thyroid autoimmunity-negative (mean age, 30.9 years) women with infertility. Thyroid autoimmunity was defined as a serum thyroperoxidase concentration of at least 34 IU/mL or a thyroglobulin concentration of at least 115 IU/mL. All participants underwent their first complete IVF or intracytoplasmic sperm injection cycle between April 2016 and February 2022. Researchers compared embryo quality measurements and clinical outcomes between those with and without thyroid autoimmunity.
Researchers observed no significant differences between participants with and without thyroid autoimmunity in the high-quality cleavage embryo rate (52.8% vs. 53.4%; P = .66) and cumulative live birth rate (53.4% vs. 56.2%; P = .31). In addition, researchers noted no significant differences between those with and without thyroid autoimmunity in rates of oocyte retrieval (69.1% vs. 69.4%; P = .65), fertilization (61.1% vs. 62.2%; P = .34), embryo utilization (80.2% vs. 80.8%; P = .61), blastocyte formation (48.5% vs. 48.4%; P = .97) and high-quality blastocysts (29.9% vs. 29.4%; P = .73).
Clinical pregnancy rate (46.7% vs. 44.6%; P = .4), early pregnancy loss rate (13.5% vs. 11.5%; P = .44) and live birth rate (37.4% vs. 36%; P = .55) of the first transfer cycle were also not significantly different between participants with and without thyroid autoimmunity.
“These findings need to be confirmed in large prospective studies,” the researchers wrote.
Perspective
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Rao and colleagues conducted a retrospective study to investigate the impact of thyroid autoimmunity on embryo quality and pregnancy outcomes in patients undergoing IVF, in which the egg and sperm are left to fertilize in a petri dish, or intracytoplasmic semen injection, in which the sperm is directly injected into the egg. The study compared 499 thyroid autoimmunity-positive and 2,945 thyroid autoimmunity-negative euthyroid women whose first oocyte retrieval cycle resulted in live birth after embryo transfer or failed to result in live birth after all embryos were transferred.
The reason for the study is that data have been mixed as to the significance of thyroid autoimmunity and its effects on fertility and assisted reproductive technology (ART) outcomes. Some studies have shown increased risks of pregnancy loss and preterm birth in women with thyroid autoimmunity while others have not supported these findings. The 2017 American Thyroid Association thyroid and pregnancy guidelines recommend treating patients with TSH above 2.5 mIU/L undergoing ART but does not have any specific recommendations regarding patients with thyroid autoimmunity in the preconception period.
The study results showed no significant difference in embryo quality or cumulative live birth rate, defined as the rate of live births per oocyte retrieval cycle, following IVF/intracytoplasmic semen injection. Strengths of this study include it being the first study to investigate the association between thyroid autoimmunity and cumulative live birth rate. In addition, it is a large cohort study conducted at a single center looking at the effect of thyroid autoimmunity on embryo quality. Weaknesses of the study include its retrospective design, the absence of population-specific reference ranges, small sample sizes in the subgroup analyses and absence of etiologies of infertility.
Nevertheless, the study results are clinically important because they add to the growing number of studies that suggest thyroid autoimmunity in the absence of hypothyroidism does not have a detrimental effect on ART outcomes. Prior studies have suggested that the increased use of intracytoplasmic semen injection may help explain the conflicting results in the literature suggesting intracytoplasmic semen injection may be preferred in patients with thyroid autoimmunity. However, in this study, there was no significant difference in the subgroup analysis comparing IVF and intracytoplasmic semen injection methods.
Notably, the study excluded patients with recurrent pregnancy loss of at least two times. The authors explain that this is because such patients may be more susceptible to thyroid autoimmunity, referencing recent studies that have demonstrated in patients with recurrent pregnancy loss, thyroid autoimmunity was associated with significantly lower live birth rate compared with those without thyroid autoimmunity and treatment with levothyroxine resulted in similar live birth rate to thyroid autoimmunity-negative women.
Once pregnant, patients with thyroid autoimmunity have a blunted response in thyroxine levels compared to thyroid autoimmunity-negative patients and may be at risk for inadequate thyroid hormone production in pregnancy. Seven percent to 20% of euthyroid patients with thyroid autoimmunity preconception develop elevated TSH in pregnancy. However, in this study, thyroid hormone levels after embryo implantation and throughout pregnancy were not reported.
Overall, the results of this study suggest that thyroid autoimmunity alone may not affect embryo quality and cumulative live birth rate in general patients presenting for IVF/intracytoplasmic semen injection, but that this should not be extended to patients with a history of recurrent pregnancy loss for whom thyroid autoimmunity may play a more significant role.
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