Comparative analysis of long versus short co-incubation of gametes on post-insemination outcomes and embryo morphokinetics.

Research Question: Does a short co-incubation of gametes in conventional IVF affect post-insemination outcomes and embryo morphokinetics?

Design: Sibling oocyte randomized pilot study conducted between December 2020 and March 2023. Eligible couples (n = 55) were women aged 18-43 years with BMI 35 km/m or lower and male normal semen parameters. Cumulus oocyte complexes (COC) (six to 12) were randomized in a 1:1:2 proportion in long (16-18 h) or short (2 h) co-incubation IVF exposure and ICSI, respectively. All oocytes inseminated via IVF were monitored by time-lapse. Blastocysts graded BL3CC or higher underwent trophectoderm biopsy on days 5, 6 or 7, and were analysed by next-generation sequencing.

Results: A total of 954 COC were distributed to long co-incubation (n = 235 [24.6%]), short co-incubation (n = 235 [24.6%]) and ICSI (n = 484 [50.7%]). In total, 202 were MII after long co-incubation, 209 after short co-incubation and 394 at ICSI. Regression analyses showed that short co-incubation groups (OR 0.72, 95% CI 0.46 to 1.11, P = 0.139) and ICSI (OR 1.43, 95% CI 0.95 to 2.15, P = 0.090) did not significantly affect normal fertilization rates (2PN) compared with long co-incubation. Usable blastocysts per MII, per 2PN, and euploid blastocysts per MII, per 2PN and per tested blastocysts were similar among the groups. The rate of embryo arrest (hazard ratio [HR] 0.79, 95% CI 0.57 to 1.11, P = 0.183) and timings to reach morphokinetic milestones among embryos reaching blastulation were similar between IVF groups (P > 0.05 for all).

Conclusion: A short 2-h co-incubation of gametes in IVF yields comparable fertilization, blastocyst and euploidy rates without adverse embryo morphokinetic events, compared with standard overnight co-incubation.