How Low Can You Go? Transfer of Low-Grade Blastocysts

Abstract

Background: Low grade blastocyst (LGB) transfer results in varied live birth rates (5-39%). Only limited studies with small sample sizes (n=10-440) exist, due to LGB transfer being less desirable. Definitions of LGB and study designs are heterogenous, further confounding outcome interpretation. Aim: This study aimed to obtain sufficient LGB transfers to determine live birth rates, as well as allow subgroup analysis by blastocyst quality and maternal age. Method: This study was a multicentre, multinational retrospective cohort study across nine IVF clinics in China and New Zealand between 2012 to 2019. 6966 single blastocyst transfer cycles on days 5-7 (fresh and frozen) were collected; of these, 875 transfers were from LGBs (<3BB). Blastocysts with expansion stage 1 or 2 (early blastocysts) were excluded. The main outcome was live birth rate. Blastocysts were grouped according to quality grade: good-grade blastocysts (GGBs; n=3849, AA, AB and BA), moderate-grade blastocysts (MGBs; n=2242, BB) and LGBs (n=875, AC, CA, BC, CB and CC). Live birth rates were compared using the Pearson Chi-squared test. A logistic regression analysis examined the relationship between blastocyst grade and live birth after adjustment for confounders: clinic, female age, expansion stage, and blastocyst age. Results: Live birth rates for GGBs, MGBs and LGBs were 45%, 36% and 28% respectively (p<0.0001). Within the LGB group, the highest live birth rates were for grade C TE (30%) and the lowest were for grade C ICM (19%). The lowest combined grade (CC) had a 15% live birth rate (n=7/48). The odds of live birth were 2.33 (95% CI = 1.88-2.89) for GGBs compared to LGBs and 1.56 (95% CI = 1.28-1.92) for MGBs compared to LGBs following fresh and frozen blastocyst transfers (p<0.0001). The odds of live birth according to ICM grade were 1.31 (A versus B; 95% CI = 1.15-1.48), 2.82 (A versus C; 95% CI = 1.91-4.18) and 2.16 (B versus C; 95% CI = 1.48-3.16; all p<0.0001). The odds of live birth according to TE grade were 1.33 (A versus B; 95% CI = 1.17-1.50, p<0.0001), 1.85 (A versus C; 95% CI = 1.45-2.34, p<0.0001) and 1.39 (B versus C; 95% CI = 1.12-1.73, p=0.0024). Conclusion: The live birth rate for LGBs is 28%, with rates ranging between 15-31% for the different inner cell mass (ICM) and trophectoderm (TE) subgroups of LGBs. Even those in the lowest grading tier maintain modest live birth rates (15%; CC). Thus, these can be considered for transfer in women with few other options.