Morethanjust ploidystatus: dayof vitrification and inner cell mass grade are associated with live birth in euploid embryos

To determine if day of blastocyst development, inner cell mass (ICM), or trophectoderm (TE) grade is associated with pregnancy outcomes in euploid embryos. A single-center retrospective cohort analysis of all patients undergoing single frozen embryo transfer (FET) following autologous IVF with PGT-A from 2020-2021 was conducted. Blastocysts underwent biopsy for PGT-A and were vitrified on day 5 or 6 of embryo development. Before vitrification, the ICM and TE of each embryo were graded as 1 (good), 2 (fair) or 3 (poor). The primary outcome analyzed was live birth (LB). Mixed-effect multivariable logistic regression was used to assess the association of LB with day of blastocyst development and embryo grade. A p-value of <0.05 was considered statistically significant. Data were collected from 768 euploid FET cycles (576 patients). The mean age and BMI at FET were 36.3 years and 25.9 kg/m2, respectively. After FET, pregnancy did not occur in 29.8% of all cycles, 15.4% of cycles ended in an early pregnancy loss and 52.6% of cycles resulted in LB. Table 1 depicts outcomes after FET stratified by day that the blastocyst stage was reached, as well as ICM and TE grades. Of all FETs analyzed, 63.0% of embryos were vitrified on day 5 while 36.8% were vitrified on day 6. Blastocysts biopsied and vitrified on day 6 demonstrated lower odds of LB than those vitrified on day 5 (aOR 0.78, 95% CI 0.65-0.94). At vitrification, 82.0% of embryos had a grade 1 ICM and 18.0% had grade 2 or 3. Embryos with grade 2 or 3 ICM had significantly lower odds of LB than embryos with grade 1 (aOR 0.74, 95% CI 0.58-0.94). Regarding TE, 63.6% of embryos were grade 1 and 36.4% were grade 2 or 3. There was no significant difference in odds of LB between embryos with grade 1 TE versus those with grade 2 or 3 (aOR 0.99, 95% CI 0.82-1.19).Tabled 1Table 1: Pregnancy outcomes by day vitrified and gradeNot pregnant, % (n)Pregnancy Loss, % (n)Live birth, % (n)Vitrified day 5 (n=482)23.4% (113)16.6% (80)57.3% (276)Vitrified day 6 (n=282)39.7% (112)13.5% (38)45.4% (128)ICM grade 1 (n=628)28.5% (179)14.0% (88)55.6% (349)ICM grade 2 or 3 (n=138)34.8% (48)21.7% (30)39.9% (55)TE grade 1 (n=487)27.9% (136)15.8% (77)54.0% (263)TE grade 2 or 3 (n=279)32.6% (91)14.7% (41)50.5% (141) Open table in a new tab Euploid embryos that reached the blastocyst stage on day 5 had significantly higher odds of LB compared to embryos that reached the blastocyst stage on day 6. Furthermore, euploid embryos with grade 1 ICM were significantly more likely to result in LB than those with grade 2 or 3 ICM. TE grade was not associated with odds of LB.