Discussion
sex-linked diseases
Since the advent of ART, many attempts have been made to accurately select offspring sex. However, most of the techniques that have been used are cumbersome, ineffective, and/or raise safety concerns. The ethics of embryo sex selection is an ongoing debate, but we believe that sex selection of spermatozoa is more ethically acceptable. However, evidence of clinical efficacy and safety is crucial. Therefore, in this study, we included a control group consisting of couples undergoing ICSI/PGTA for reasons other than sex selection.The current literature on sperm sex selection is limited by the lack of studies that simultaneously assess a method’s technical efficacy, clinical reliability, and safety. Moreover, most sex selection studies are performed in livestock, with many yielding modest or inconsistent results. For instance, a study carried out on bovine spermatozoa processed by the Percoll method excluded a confirmatory FISH sperm assessment and did not appear to evidence sex-enriched embryos [To address the questions left unanswered by previous studies, we aimed to carry out a thorough assessment of our sex selection method. Upon FISH comparison of the processed sperm specimens from the control and study cohorts, we found that our method was consistently able to enrich spermatozoa according to gonosome. We then carried out an assessment to confirm the clinical efficacy of these sex-enriched sperm specimens, and observed that the proportion of tested embryos maintained the sex enrichment.Following these encouraging findings, we aimed to evaluate the clinical performance of the spermatozoa by comparing ICSI outcomes of the ICSI/PGTA+GS cohort to those from the control group. A recent meta-analysis performed on data obtained from bovine sperm sex selection studies demonstrated that the overall pregnancy and calving rates decreased in cases where sexed sperm specimens were used [To determine whether our sex selection method affects reproductive outcome, we compared the ICSI results between cohorts, stratifying by the couples’ desired offspring sex. Fertilization, implantation, clinical pregnancy, and delivery rates were not significantly impaired.The last, and most important, aspect of our assessment is on the safety of our proposed method. Previous studies, particularly those on flow cytometry, have expressed concern about the mutagenic effects of the UV light and DNA binding agent [In this study, we propose a novel and safe sex selection method that is able to consistently skew the proportion of spermatozoa toward the desired sex for couples undergoing ICSI. Along with the medical rationale of avoiding sex-linked diseases, the scientific rationale for developing our sperm-based sex selection technique is to provide a more ethical procedure to successfully skew the proportion of conceptuses towards a couple’s desired sex without impairing embryo developmental competence or offspring health. Nevertheless, this study is not without limitations. While we were successfully able to maintain the sex enrichment achieved in spermatozoa, embryos were still arbitrarily selected. Thus, a prospective randomized study should be performed as a follow-up assessment to confirm findings. In addition, despite the efficacy demonstrated, there were rare occurrences where all tested conceptuses were of the opposite sex than what we selected for. This may be attributed to subtle morphological and functional differences between the X- and Y-bearing spermatozoa post-selection. Although we did not observe any differences in overall sperm morphology between the cohorts, we cannot exclude that these morphological properties may have influenced the ICSI operator to obviate the sex enrichment by choosing the best-looking spermatozoon at the time of injection.Although our sperm sex selection method does not necessarily guarantee offspring of a specific sex, couples participating in the study were nonetheless able to obtain a greater proportion of spermatozoa and conceptuses of their desired gonosomal component. Comparisons of ICSI clinical outcomes also showed that fertilization rates and embryo developmental competence were not impaired by using sex-enriched sperm specimens. Moreover, offspring health was not negatively affected. These encouraging findings indicate that not only is our method effective, but also safe, rendering it a feasible and ethically palatable procedure.