The extent of paternal effect: the blastocyst matters! A retrospective analysis of 1351 single, frozen-thawed embryo-transfers

Study question Is ongoing pregnancy rate (OPR) impaired by total motile count (TMC) values in IVF/ICSI cycles? Summary answer TMC does not affect the OPR in IVF/ICSI cycles. What is known already Studies exploring the paternal role and specifically the influence of sperm parameters on the IVF/ICSI outcomes led to contradictory results, especially after the blastocysts formation. If a negative impact of severe male infertility on fertilization rate, embryo morphology and blastocyst formation rate have been described by several studies, its effect on implantation rate (IR), OPR and live birth rate (LBR) is still debated. In this context, TMC is an useful and validated tool for sperm evaluation, combining three critical sperm parameters into a single indicator of sperm quality. Study design, size, duration Retrospective analysis of 1351 freeze-all IVF/ICSI cycles performed between January 2015 and June 2022 in the Reproductive Sciences Unit of Gynaecology/Obstetrics Department of San Raffaele Hospital in Milan, Italy. Participants/materials, setting, methods We included all the first, single, frozen-thawed transfers performed in the study period. Transfers of blastocysts obtained by frozen semen were excluded. Couples’ characteristics, semen parameters and controlled ovarian stimulation data were collected. Semen quality was assessed using TMC and grouped into quartiles of TMC for the analyses. The primary outcome of the study was the evaluation of the effect of TMC on the implantation potential of the obtained blastocysts. Main results and the role of chance 1351 transfers were analyzed. Performing a logistic regression analysis adjusted for confounding factors (maternal age, number of oocytes retrieved and quality of transferred blastocysts), OPR was not influenced by TMC values [odds ratio (OR) = 1.00; confidence interval (CI) = 0.99-1.00; p = 0.5]. After grouping the male infertility population into quartiles of TMC, no significant differences in OPR were found between extreme quartiles (n = 339, TMC ≤4 million and n = 348, TMC ≥42 million respectively), even when adjusted for confounders [OR = 0.99; CI 0.73-1.35; p = 0.97]. Therefore, the implantation potential of the obtained blastocysts, once formed, seems to be independent from the sperm quality. Limitations, reasons for caution The major limitation of the study is the retrospective design. Additionally, although a positive correlation between TMC and pregnancy rate is well described, a TMC threshold for defining severe male infertility has not been yet identified. Wider implications of the findings With a larger sample size we confirmed the results of our previous study. Indeed, TMC did not demonstrated to impair OPR of blastocysts from infertile couples submitted to IVF/ICSI. Further data, such as pregnancy and obstetrics outcomes, would be necessary to better define the role of male infertility in reproduction. Trial registration number Not applicable