Abstract Purpose To investigate whether alignment among zygotic cleavage plane (CP), pronuclear (PN) axis, and polar axis (PB) is associated with a higher live birth rate (LBR) in single transferred blastocysts. Methods A total of 103 fresh and 138 frozen blastocysts generated via either conventional IVF insemination or intracytoplasmic sperm injection (ICSI) using fresh autologous oocytes between September 2022 and December 2023 were retrospectively analyzed. LBRs were compared according to alignment among three zygotic axes. The PN axis was defined by the longitudinal axis before fading, and the PB axis was determined by the position of the second polar body. Alignment relative to the zygotic CP was classified as CPPN+ or CPPN- for the PN axis, and CPPB+ or CPPB- for the PB axis. Results In the fresh transfer dataset, the highest LBR was observed in CPPN+/CPPB+ blastocysts (77.5%), compared with CPPN+/CPPB- (20.0%, P < 0.001), CPPN-/CPPB+ (15.2%, P < 0.001), and CPPN-/CPPB- (6.7%, P < 0.001). Similar patterns were observed in the frozen transfer dataset, where CPPN+/CPPB+ blastocysts again had the highest LBR (48.3%), compared with CPPN+/CPPB- (16.1%, P = 0.003), CPPN-/CPPB+ (19.4%, P = 0.007), and CPPN-/CPPB2- (11.1%, P = 0.005). Logistic regression confirmed CPPN and CPPB alignment as independent predictors of live birth in both datasets, after adjusting for several potential confounders. Conclusion Our findings provide preliminary evidence to support zygotic alignment among CP, PN, and PB axes as a potential live birth marker for blastocyst selection.
LIU et al. (2026) studied this question.