54 Assessment of the viability of four morphokinetic categories of blastocysts: Preliminary results

Videomicroscopy allows observation of early morphokinetic parameters in the in vitro-produced (IVP) embryos. Reis et al. (2018 Proc. of the 34th Annual Meeting A.E.T.E, Nantes, September) proposed a classifier for IVP embryos based on combinations of 27 early morphokinetic parameters (observed before the fourth embryonic cycle) and supervised machine learning (random forest). Four categories of blastocysts were defined: early hatching blastocysts (EHBs), hatching blastocysts (HB), delayed blastocysts (DBs), and arrhythmic blastocysts (ABs). The present work was designed to assess the viability of these morphokinetic categories under field conditions. Embryos were produced in vitro from ovum pickup oocytes collected from 30 Holstein heifers (PH) fertilized with frozen-thawed semen of five PH bulls (Reis et al. 2023 Reprod. Fertil. Dev. 36, 179–180). At Day 6 and Day 7, embryos having reached the desired stage of expansion (inner zona pellucida [ZP] diameter > 135 µm and ZP > 2 µm thinner) were slow frozen. Embryos were classified using the morphokinetic classifier (Reis et al. 2018), then thawed and blind transferred individually by 11 operators into heifers (Day 7 after routine synchronization protocol) at 41 commercial farms. Each farm received at least one embryo of each morphokinetic category. Ultrasound pregnancy diagnostic (PD) was systematically performed at 45–60 days post-heat. Birth and calf survival were recorded 48 h after birth. Pregnancy rate (PR = n pregnant at PD/n transferred), birth rate (BR = n calves born/n embryos transferred), survival rate (SR = n alive calves at 48 h/n born), and overall performance (OP = n alive calves/n embryos transferred) were calculated. In total, 285 blastocysts were transferred and 63 calves survived after birth. The results of PR, BR, and OP were compared using chi-squared, and the results of SR were compared with Fisher’s exact test (confidence level, 95%). The detailed results for EHBs, HBs, DBs, and ABs were respectively: PR (P = 0.65): 29.4% (15/51), 39.5% (32/81), 37.1% (29/78), and 33% (25/75); BR (P = 0.46): 19.6% (10/51), 32.1% (26/81), 26.9% (21/78), and 25.3% (19/75); SR (P = 0.18): 100% (10/10), 84.6% (22/26), 85.7% (18/21), and 68% (13/19); and OP (P = 0.48): 19.6% (10/51), 27.2% (22/81), 23.1% (18/78), and 17.3% (13/75). In summary, we observed up to 9.9% of OP variation between these morphokinetic categories. EHBs and ABs presented less than 20% OP. EHBs had the lowest PR but the highest SR, and ABs presented intermediate PR but the lowest SR. According to the results of this exploratory study, it would be necessary to multiply the number of embryos transferred by two or four to demonstrate statistical differences for SR or BR and OP, respectively. Despite the lack of statistical power, this study is encouraging because these results suggest that the different morphokinetic categories could have different impacts on the performance of IVP operations. It could be particularly quantified in large-scale operations. A more in-depth analysis of the results of this study is currently underway.

This research was funded by APIS-GENE.