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Title

The predictive value of post warming morphokinetic factors for embryo implantation

Objective

Even though the initial blastocyst survival rate after vitrification and warming surpasses 90%, vitrified human blastocysts show varied re-expansion capacity after warming and little is known about the effect of embryo behavior after warming on implantation potential. Therefore, the goal for the present study was to investigate whether frozen-thawed blastocyst morphokinetics, observed using time-lapse imaging (TLI), may be an indicator for implantation in intracytoplasmic sperm injection (ICSI) cycles, with deferred embryo transfers (freeze-all cycles).

Methods

From January to October/2022, an observational cohort study was conducted at a private university-affiliated IVF center. This included 411 vitrified/warmed blastocysts with known implantation data (no implantation and full implantation per transfer), which were evaluated by TLI. Blastocysts were incubated in EmbryoScope+ (Vitrolife, Denmark) for up to 4 hours, immediately after warming until transfer. Blastocysts morphological dynamics variables after warming were recorded, and their potential association with clinical pregnancy were investigated. The recorded variables were: (i) the initial blastocyst area (IBA) and zona pellucida thickness (IZP) immediately after warming, (ii) the maximum blastocyst area (MBA) and the minimum ZP thickness (MZP) immediately before transfer, and (iii) expansion (whether the embryo re-expands or not after warming). Embryos were split into percentiles groups according to the values of IBA, MBA, IZP, and MZP. For each parameter, values below the 33rd percentile, between the 33rd and the 67th percentile, and values above the 67th percentile were recorded. Embryos received a final score from 0 to 9, according with the sum of the scores from each parameter, in each percentile, and the influence of the score on embryos implantation was evaluated.

Results

The average maternal age in the study population was 37.4 ± 5.0 years old. The after warming factors values divided according with < 33rd percentile, from 33rd to 67th percentile, and > 67th percentile were respectively: IBA: 9611.1 µm2, 11851.4 µm2, and 26845.0 µm2; MBA: 14110.0 µm, 18572.6 µm2, and 93381.0 µm2; IZP: 13.0 µm, 16.0 µm, and 28.0 µm, and MZP: 11.0 µm, 14.0 µm, and 23.0 µm. No significant effect of after warming parameters on implantation results were observed when the parameters were individually evaluated. Clinical outcomes are given in Table 1. A significant increase in the implantation rate was noted among embryos presenting higher scores, followed by those with median scores, while embryos with lower scores presented the lowest implantation rate. Miscarriage rates tended to be higher in the low and medium total score groups compared to high total score group, however statistical significance was not reached. The logistic regression analysis showed that embryos in the low total score group present a 12.3% decreased chance of implantation when compared with embryos in the high total score group (OR: 0.877, CI: 0.843 - 0.912, p<0.001), while embryos in the medium total score group presents a 9.6% decreased implantation chance when compared with embryos in the high score group (OR: 0.904, CI: 0.870 - 0.939, p<0.001).

Conclusion

The blastocyst behavior after warming, by evaluating the blastocyst area, the ZP thickness, and re-expansion, together with the pre-vitrification embryo classification may provide important information for selecting the best embryo for transfer or in managing the patient´s expectations.

Keywords

Embryo development; frozen-thawed embryo transfer; implantation; Time-lapse microscopy.

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