Increased blastomere number in D3 embryos is associated with higher live birth rates in vitrified– thawed single blastocyst transfer cycles

Abstract

Background The number of D3 embryo blastomeres affects pregnancy outcomes in patients undergoing cleavage-stage embryo transfer. However, the association between blastomere number in D3 embryos and pregnancy outcomes after vitrified–thawed single blastocyst transfer remains unknown.Methods This retrospective cohort follow-up study included 2,274 cases of vitrified–thawed single blastocyst transfer,all patients were divided into six groups according to blastomere number of D3 embryos: ≤5, 6, 7, 8, 9, and ≥ 10 cells. The primary outcome was the live birth rate (LBR). The secondary outcomes were the clinical pregnancy rate, miscarriage rate, and neonatal outcomes. Statistical analyses were performed using a multivariate logistic regression model to explore the association between blastomere number in D3 embryos and LBR.Results The LBR significantly increased with the number of blastomeres in D3 embryos (28.4%, 36.4%, 42.5%, 46.1%, 45.2%, and 58.1%; p < 0.001). Furthermore, the results of the high- and low-quality blastocyst subgroup analyses showed significant differences in the LBR among the groups (p < 0.01). As the number of blastomeres in D3 embryos increased, the miscarriage rate significantly decreased (23.3%, 18.6%, 14.0%, 15.9%, 13.6%, and 8.9%; p < 0.05). However, the number of blastomeres did not affect perinatal outcomes. Multivariate logistic regression analysis after adjusting for confounding factors revealed significantly decreased LBR in the ≤ 5-cell group (adjusted odds ratio [aOR]: 0.627, 95% confidence interval [CI]: 0.442–0.891; p < 0.01) and significantly increased LBR in the ≥ 10-cell group (aOR: 1.612, 95% CI: 1.230–2.112; p < 0.01) compared with that in the 8-cell group.Conclusions The number of blastomeres in D3 embryos may be an important factor in selecting blastocysts during vitrified–thawed single blastocyst transfer cycles. The transfer of a single blastocyst arising from ≥ 10-blastomere D3 embryo may reduce the miscarriage rate and improve LBR.