Association between hatching status and pregnancy outcomes in single blastocyst transfers: a retrospective cohort...

To examine the potential association between blastocyst hatching status and pregnancy outcomes following single blastocyst transfer.

This is a retrospective cohort. We screened all frozen-thawed single blastocyst transfer cycles from January 1, 2020, to April 30, 2022, at the authors' center. The hatching status was graded into four categories: unhatched, early hatching (hatched portion < the diameter of zona pellucida), late hatching (hatched portion > the diameter of zona pellucida), and fully hatched. Multivariate logistic regression was used to examine the association between hatching status and pregnancy outcomes (clinical pregnancy and live birth).

The final analysis included 906 cycles. The hatching status was unhatched in 116 cycles, early hatching in 556 cycles, late hatching in 197 cycles, and fully hatched in 37 cycles. The clinical pregnancy rate was 54.3%, 63.3%, 74.6%, and 54.1%, respectively (p = 0.001) in the unhatched, early-hatching, late-hatching, and fully hatched groups, respectively. The live birth rate was 39.7%, 51.6%, 58.3%, and 40.5%, respectively (p = 0.008). In pairwise comparisons, the late-hatching group had significantly higher rates of clinical pregnancy and live birth versus the unhatched category (p = 0.001 and p = 0.008, respectively). In multivariate logistic regression analysis, embryo hatching status, the duration until blastocyst formation, the grading of blastocyst cells, and the thickness of the endometrium were associated with clinical pregnancy and live birth.

After adjusting for confounding factors, late-hatching status of the blastocysts was associated with a higher rate of clinical pregnancy and live birth.