TABLE 2.
Patient and cycle characteristics of the matched day 3, day 5, day 6, and day 7 vitrified-warmed embryo transfer groups.
| Characteristics | Day 3 | Day 5 | Day 6 | Day 7 | P-valuea | P-valueb | P-valuec |
| Age (years) | 32 (29, 34) | 31 (28, 34) | 32 (29, 35) | 31 (29, 34) | 0.876 | 0.601 | 0.931 |
| BMI (kg/m2) | 21.0 (19.5, 22.9) | 20.8 (19.5, 22.6) | 20.8 (19.5, 22.5) | 20.7 (19.6, 22.6) | 0.632 | 0.986 | 0.875 |
| Duration of infertility (years) | 3 (2, 5) | 3 (2, 5) | 3 (2, 5) | 3 (2, 5) | 0.570 | 0.741 | 0.785 |
| Gravidity | 0 (0, 1) | 0 (0, 1) | 0 (0, 1) | 1 (0, 1) | 0.643 | 0.837 | 0.723 |
| Parity | 0 (0, 0) | 0 (0, 0) | 0 (0, 0) | 0 (0, 0) | 0.901 | 0.918 | 0.845 |
| FET rank | |||||||
| First | 196 (70.3) | 195 (69.9) | 183 (65.6) | 65 (69.9) | 0.948 | 1 | 0.446 |
| Higher rank | 83 (29.7) | 84 (30.1) | 96 (34.4) | 28 (30.1) | |||
| Main infertility cause (%) | 0.647 | 0.882 | 0.830 | ||||
| Female | 145 (52.0) | 157 (56.3) | 157 (56.3) | 50 (53.8) | |||
| Male | 47 (16.8) | 29 (10.4) | 38 (13.6) | 11 (11.8) | |||
| Mixed | 67 (24.0) | 80 (28.7) | 65 (23.3) | 26 (28.0) | |||
| Other | 20 (7.2) | 13 (4.7) | 19 (6.8) | 6 (6.5) | |||
| Endometrial preparation (%) | 0.526 | 0.887 | 0.440 | ||||
| Natural cycles | 64 (22.9) | 71 (25.4) | 87 (31.2) | 26 (28.0) | |||
| Hormone therapy cycles | 121 (43.4) | 107 (38.4) | 85 (30.5) | 35 (37.6) | |||
| Stimulated cycles | 94 (33.7) | 101 (36.2) | 107 (38.4) | 32 (34.4) | |||
| Cycles with ICSI (%) | 127 (45.5) | 129 (46.2) | 123 (44.1) | 43 (46.2) | 0.904 | 1 | 0.718 |
| Endometrial thickness on ET day (mm) | 10.3 (9.1, 11.9) | 10.3 (9.2, 11.8) | 10.5 (9.1, 12.1) | 10.2 (9.1, 12.3) | 0.738 | 0.797 | 0.872 |
| No. of embryo transferred | 0.673 | 0.630 | 0.904 | ||||
| 1 | 157 (56.3) | 158 (56.6) | 148 (53.0) | 50 (53.8) | |||
| 2 | 122 (43.7) | 121 (43.4) | 131 (47.0) | 43 (46.2) | |||
| Year of treatment (%) | 0.770 | 0.438 | 0.863 | ||||
| 2006–2011 | 74 (26.5) | 66 (23.7) | 77 (27.6) | 28 (30.1) | |||
| 2012–2013 | 75 (26.9) | 87 (31.2) | 79 (28.3) | 25 (26.9) | |||
| 2014–2017 | 130 (46.6) | 126 (45.2) | 123 (44.1) | 40 (43.0) |
FET, frozen embryo transfer. ET, embryo transfer. Data are presented as mean (±SD) or median (first quartile, third quartile) according to if variables were normally distributed or not. Continuous variables were compared using t-test or Mann–Whitney–Wilcoxon tests, and categorical variables were presented as numbers (%) and evaluated with Chi-squared tests. aP-value for day 3 vs. day 7. bP-value for day 5 vs. day 7. cP-value for day 6 vs. day 7.