Comparison of early and fully expanded blastocysts on pregnancy and birth outcomes in patients with fresh IVF/ICSI cycles: A retrospective cohort study

Objective To investigate the effect of the early blastocyst on pregnancy and birth outcomes in patients in vitro fertilization/(early rescue) intracytoplasmic sperm injection-embryo transfer [IVF/(early rescue)ICSI-ET] cycles. Methods In this retrospective cohort study, 289 patients with single-blastocyst transfer within IVF/(early rescue)ICSI-ET treatment cycle were included and divided into the early (n = 48, Gardner stage = 1 or 2) and the fully expanded blastocyst (n = 241, Gardner stage >= 3) groups. The differences in pregnancy and birth outcomes between the two groups were compared. Results There was no significant differences between the two groups in baseline indicators, including demographic characteristics and clinical treatment (P> 0.05).The clinical outcomes indicators in the early and the fully expanded blastocyst groups were compared, including the number of transferable embryos on the third day (D3)5.0 (4.0, 6.8) vs. 6.0 (5.0, 8.0) (P = 0.001), the number of remaining embryos frozen per cycle 1.0 (0.3, 2.0) vs. 3.0 (2.0, 5.0) (P<0.001); the number of cycles of unfrozen embryos 13/48 (27.1%) vs. 12/241 (5.0%) (P<0.001); the pregnancy outcome including the clinical pregnancy rate (CPR) 20/48 (41.7%) vs. 129/241 (53.5%) (P>0.05); the live birth rate (LBR)15/48 (31.3%) vs.106/241 (44.0%) (P>0.05). There were no significant differences in birth outcomes, such as gestational week of labor, mode of delivery, neonatal birth weight, height, Apgar score, sex ratio, and birth defects between the two groups (P>0.05).Multivariate binary logistic regression showed the same result, i.e., early blastocyst transfer in fresh cycle was not a risk factor for clinical pregnancy (OR = 0.516, 95% CI = 0.260-1.022) and live birth (OR = 0.521, 95% CI = 0.252-1.079). Conclusion Compared with the fully expanded blastocyst group, the CPR and LBR in the early blastocyst group of the fresh transfer cycles were relatively ideal, and there were no significant differences in birth outcomes and neonatal status between the two groups.