The Valuable Reference of Live Birth Rate in the Single Vitrified-Warmed BB/BC/CB Blastocyst Transfer: The Cleavage-Stage Embryo Quality and Embryo Development Speed

It is unclear whether we should focus attention on cleavage-stage embryo quality and embryo development speed when transferring single particular grade vitrified-warmed blastocysts, especially poor-quality blastocysts (grade "C").

This retrospective study considered 3386 single vitrified-warmed blastocyst transfer cycles from January 2010 to December 2017. They were divided into group 1 (AA/AB/BA, n = 374), group 2 (BB, n = 1789), group 3 (BC, n = 901), and group 4 (CB, n = 322). The effects of cleavage-stage embryo quality and embryo development speed were measured in terms of clinical pregnancy and live birth rates in each group.

Pregnancy outcomes showed a worsening trend from groups 1 to 4; the proportion of embryos with better cleavage-stage quality and faster development speed decreased. In group 1, only the blastocyst expansion degree 3 was a negative factor in the clinical pregnancy rate (odds ratio (OR) [95% confidence interval (CI)]: 0.233 [0.091-0.595]) and live birth rate (0.280 [0.093-0.884]). In the other groups (BB, BC, and CB), blastocysts frozen on day 5 had significantly better clinical pregnancy outcomes than those frozen on day 6: 1.373 [1.095-1.722] for group 2, 1.523 [1.055-2.197] for group 3, and 3.627 [1.715-7.671] for group 4. The live birth rate was 1.342 [1.060-1.700] for group 2, 1.544 [1.058-2.253] in group 3, and 3.202 [1.509-6.795] in group 4, all Ps < 0.05). The degree of blastocoel expansion three for clinical pregnancy rate in group 2 (0.350 [0.135-0.906], P < 0.05) and day 3 blastomere number (>7) for live birth rate in group 4 (2.455 [1.190-5.063], P < 0.05) were two important factors.

We should consider choosing BB/BC/CB grade blastocysts frozen on day 5, CB grade blastocysts with day 3 blastomere numbers (>7), and AA/AB/BA grade blastocysts with degrees of expansion (≥4) to obtain better pregnancy outcomes.