Table 3.

Comparison of fresh ET and FET cycles using slow-growing embryos

Characteristic	Fresh cycles (n = 531)	Thaw cycles (n = 623)	P-value
Maternal age (years)	37.29	36.41	0.0016
Body Mass Index (kg/m${}^2$)	25.32	25.11	0.5264
ICSI (%)	70.62	67.42	0.241
Grade of embryo (mean)	1.89	1.89	0.984
Grade of embryo
Grade 1 (%)	34.65	33.87	0.968
Grade 2 (%)	42.75	44.14	0.968
Grade 3 and above (%)	22.03	21.51	0.968
Cumulative ET	1.39	2.97	$<$ 0.0001
Clinical pregnancy (%)	8.10	7.22	0.577
Life birth (%)	6.40	6.26	0.921
Slow cleavage-stage embryos were defined as those embryos that had 2 pronuclei during the syngamy check at 23-24 hr and were still at the 2-cell stage at the day 2 check. For FET cycles, all embryos were at the 2-cell stage when frozen, and both cells survived the thawing process. Cumulative ET (embryo transfer) refers to previous embryo transfer cycles included in the analysis. Grade of embryos is assessed on day 2 post-insemination/ICSI for the degree of fragmentation and multinucleation. Continuous variables were examined in relation to relevant outcomes using the students t test, while binary variables were initially examined using the Chi-square test