Authors: J Matucha1, B Bopp2, M Will2, E Will2, K O’Leary2, G Adaniya1, Ovation Fertility, 1 Carmel, Indiana, USA, and Midwest Fertility Specialists, 2 Carmel, Indiana, USA

Study question
How does the embryo grade and day of vitrification affect FET outcomes from in vitro fertilization (IVF) cycles utilizing preimplantation genetic testing for aneuploidy (PGT-A)?

Summary answer
The grade of a transferred embryo affects FET outcomes in age groups differently, and Day 5 embryos have significantly better pregnancy outcomes than Day 6 embryos.

What is known already
The use of PGT-A has shown to increase implantation rates, lower miscarriage rates and promote counseling for a single embryo transfer. Although euploid embryos are the priority for transfer, it is important to examine embryo characteristics that may influence these outcomes within these euploid embryos, in order to maximize the outcome for each FET.

Study design, size, duration
In this retrospective study, 1,554 FETs transferring one euploid Day 5 or Day 6 embryo between January 2020 and October 2022 were evaluated, with the exclusion of donor oocyte, donor embryo, gestational carrier and Day 7 embryo transfer cycles. The inner cell mass and trophectoderm were each categorized as good (G), fair (F) or poor (P) respectively at the time of embryo cryopreservation. A total of 282 GG, 1,053 FG, and 209 FF embryos were transferred.

Participants/materials, setting, methods
Embryo grade categories were used to compare Day 5 vs. Day 6 transfer outcomes and by age groups. Separating groups as <34, 34-37, and ≥38 eliminated age as a significant factor. Primary outcomes included rates of positive chemical pregnancy (CP), biochemical loss (BL), clinical uterine gestation (CIG), and fetal cardiac activity (FCA). Independent t-tests compared age, and aggregate data was analyzed by proportional z-tests. A p-value <0.05 was defined as statistically significant with a 95% confidence interval.

Main results and the role of chance
Age and BL were not significant between transfer days or age groups. Day 5 had higher CP (GG: 84% vs. 65%, p<0.001; FG: 75% vs. 59%, p=0.006; FF: 63% vs. 44%, p=0.019), CIG (GG: 73% vs. 57%, p=0.006; FG: 64% vs. 48%, p<0.001; FF: 55% vs. 34%, p=0.007), and FCA (GG: 66% vs. 52%, p=0.022, FG: 60% vs. 40%, p<0.001, FF: 55% vs. 30%, p<0.001). For patients <34, GG had higher CP compared to FG and FF (74% vs. 64%, p=0.017; 74% vs. 46%, p<0.001), CIG (66% vs. 55%, p=0.011; 66% vs. 38%, p<0.001) and FCA (61% vs. 50%, p=0.012; 61% vs. 38%, p=0.001). FG had higher CP (64% vs. 46%, p=0.007) and CIG (55% vs. 38%, p=0.008) compared to FF. For patients 34-37, GG and FG had higher CP (78% vs. 53%, p<0.001; 70% vs. 53%, p=0.004), CIG (66% vs. 42%, p=0.002; 56% vs. 42%, p=0.029), and FCA (58% vs. 35%, p=0.002; 50% vs. 35%, p=0.011) compared to FF. When compared to FF in patients ≥38, GG and FG had increased CP (79% vs. 47%, p<0.001; 64% vs. 47%, p=0.012) and CIG (65% vs. 36%, p=0.004; 53% vs. 36%, p=0.010). Only GG had higher FCA (56% vs. 36%, p=0.049).

Limitations, reasons for caution
Even with the exclusion criteria, the retrospective nature of the study may be viewed as a limitation, so the significance of the results should be evaluated further.

Wider implications of the findings
Based on these results, this study demonstrates the need to compare the characteristics of euploid embryos before selection to maximize the chance of pregnancy. Embryos vitrified on Day 5 or categorized as GG, especially in patients <34, or FG should be prioritized over Day 6 or FF embryos.