Comparing day five and day six blastocyst transfers in IVF: the influence of male fertility factors on outcomes

Background: Advances in in vitro fertilization (IVF) technology now permit blastocyst transfers on both day five and day six of embryo development. However, the influence of male fertility factors on the success of these transfers is not thoroughly understood. This study aims to evaluate and compare the outcomes of day five versus day six blastocyst transfers and to explore how male fertility parameters impact IVF success rates. Methods: A prospective study was conducted over 24 months, involving 732 IVF cycles. Participants were categorized into two groups: one receiving day five blastocyst transfers (n=366) and the other receiving day six transfers (n=366). Variables such as male age, smoking habits, obesity, and semen quality were analysed. The primary outcomes-implantation rates, clinical pregnancy rates and live birth rates-were compared using chi-square and Fisher’s exact tests. Results: The success rates were notably higher for day five blastocyst transfers, with an implantation rate of 58.9% and a clinical pregnancy rate of 53.5%, compared to day six transfers, which had an implantation rate of 47.5% and a clinical pregnancy rate of 42.9%. Factors such as younger male age (<35 years), non-smoking status, normal weight and good semen quality were associated with better IVF outcomes. Conclusions: Day five blastocyst transfers generally yield higher success rates than day six transfers. Addressing male fertility factors, including age, smoking and semen quality, is essential for optimizing IVF success.