Impact of quality of the entire embryo cohort on implantation potential of the transferred blastocyst

Abstract

Despite studies focused on the association between morphology of the embryo transferred and its implantation potential, no study has evaluated the relationship between collective quality of all embryos in a given cohort and implantation rate (IR). The present study tested the hypothesis that a relationship exists between quality of the embryo cohort and IR. Retrospective cohort study. First fresh autologous IVF cycles from 05/2012 to 09/2016 with > 4 zygotes and resulting in a single blastocyst transfer were analyzed (n=819). Based on quality, each embryo was assigned a priority score (PS) of 1-8 on both day 3 and day 5 (PS of 1 having the highest presumed implantation potential). Cohorts were stratified by their mean PS; logistic regression models were used to calculate the odds ratio (OR, 95% confidence interval [CI]) of implantation (defined as viable fetus at ≥8 weeks), adjusting for patient age, body mass index, day 3 FSH, and number of embryos in the cohort. A secondary adjustment for PS of the transferred embryo was performed and a linear trend calculated. A linear decline in IR was observed as mean day 5 PS increased (test for linear trend, p=0.004; table). This effect was attenuated after adjusting for the day 5 PS of the transferred embryo (test for linear trend, p=0.66). Cohorts with ≥ 75% of embryos with day 5 PS ≥ 6 had a significantly lower IR versus those with < 75% of embryos with day 5 PS ≥ 6 (37.5% and 46.4%, respectively; [test for linear trend, p=0.04]). This effect was similarly attenuated when adjusting for the day 5 PS of the transferred embryo (test for linear trend, p=0.36). A trend was seen toward declining IR as mean day 3 PS increased, but it did not reach significance (Group A: 47.1% vs Group D: 40.9%; [test for linear trend, p=0.15]); this was also attenuated after adjusting for the day 5 PS of the transferred embryo.Tabled 1Relationship between IR of fresh day 5 single embryo transfer and the average day 5 PS of the cohortCohort group (Mean Day 5 PS)Implantation rate (Implanted/transferred)Adjusted ORAdjusted OR for day 5 PS of transferred embryoA (1.0-4.9)74/153 (51.8%)1.00 (Ref)1.00 (Ref)B (5.0 to 5.9)115/224 (47.1%)0.86 (0.57-1.30)1.01 (0.66-1.55)C (6.0 to 6.9)132/315 (41.9%)0.71 (0.47-1.06)0.98 (0.64-1.52)D (7.0 to 8.0)38/117 (32.5%)0.48 (0.29-0.80)1.06 (0.56-2.01)Linear trend, p-value0.0040.66% of cohort group with day 5 PS > 60-75271/584 (46.4%)1.00 (Ref)1.00 (Ref)> 7588/235 (37.5%)0.72 (0.53-0.99)1.10 (0.77-1.57)Linear trend, p-value0.040.36 Open table in a new tab These findings support our hypothesis that quality of all embryos in a cohort influences the IR of the transferred embryo. As quality of the entire cohort declines, the IR of the transferred embryo declines. Likewise, as the proportion of poorer quality embryos in the cohort increases, the IR declines. However, the cohort effect is attenuated when controlling for quality of the transferred embryo, suggesting that this is a more significant factor for success. Further research is warranted to determine how embryo cohort quality should be considered when deciding how many embryos to transfer.