Table 1 Baseline characteristics of immediate and delayed FET groups in the entire and propensity score-matched cohorts
Potential risk factors | Entire cohort (n = 2128) | P-value | Propensity score-matched cohort* (n = 1366) | P-value | ||
|---|---|---|---|---|---|---|
Immediate FETa | Delayed FETb | Immediate FETa | Delayed FETb | |||
(n = 1130) | (n = 998) |  | (n = 683) | (n = 683) |  | |
Maternal age (years) | Â | Â | 0.455 | Â | Â | 1.000 |
  ≤ 34 | 976 (86.4) | 851 (85.3) |  | 622 (91.1) | 622 (91.1) |  |
 35–37 | 114 (10.1) | 101 (10.1) |  | 48 (7.0) | 48 (7.0) |  |
  ≥ 38 | 40 (3.5) | 46 (4.6) |  | 13 (1.9) | 13 (1.9) |  |
BMI (kg/m2) | Â | Â | 0.431 | Â | Â | 1.000 |
  < 18.5 | 70 (6.2) | 58 (5.8) |  | 465 (68.1) | 465 (68.1) |  |
 18.5–24.9 | 750 (66.4) | 641 (64.2) |  | 22 (3.2) | 22 (3.2) |  |
  ≥ 25 | 310 (27.4) | 299 (30.0) |  | 196 (28.7) | 196 (28.7) |  |
Insemination method | Â | Â | 0.056 | Â | Â | 1.000 |
 IVF | 814 (72.0) | 681 (68.2) |  | 490 (71.7) | 490 (71.7) |  |
 ICSI | 316 (28.0) | 317 (31.8) | 193 (28.3) | 193 (28.3) | ||
COH protocol | Â | Â | 0.000 | Â | Â | 1.000 |
 GnRH-ant protocol | 485 (42.9) | 433 (43.4) | 0.273# | 284 (41.6) | 284 (41.6) | 0.651# |
  HCG trigger | 330 (68.0) | 306 (70.7) |  | 199 (70.1) | 199 (70.1) |  |
  GnRH-a trigger | 137 (28.2) | 105 (24.2) | 79 (27.8) | 79 (27.8) | ||
  Double trigger | 18 (3.7) | 22 (5.1) | 6 (2.1) | 6 (2.1) | ||
 Short acting GnRH-a protocol | 566 (50.1) | 434 (43.5) |  | 335 (49.0) | 335 (49.0) |  |
Long acting GnRH-a protocol | 79 (7.0) | 131 (13.1) | Â | 64 (9.4) | 64 (9.4) | Â |
Number of embryo transfer | Â | Â | 0.000 | Â | Â | 1.000 |
 1 | 265 (23.5) | 416 (41.7) |  | 208 (30.5) | 208 (30.5) |  |
 2 | 865 (76.5) | 582 (58.3) | 475 (69.5) | 475 (69.5) | ||
Embryo stage | Â | Â | 0.000 | Â | Â | 1.000 |
 Cleavage stage | 711 (62.9) | 499 (50.0) |  | 418 (61.2) | 418 (61.2) |  |
 Blastocyst stage | 419 (37.1) | 499 (50.0) | 265 (38.8) | 265 (38.8) | ||
Top or good quality embryo transfer | 947 (83.3) | 838 (84.0) | 0.919 | 584 (85.5) | 573 (83.9) | 0.408 |
Cause of infertility | ||||||
 Tubal factor | 720 (63.7) | 630 (63.1) | 0.778 | 456 (66.8) | 456 (66.8) | 1.000 |
 Ovulatory disorder | 304 (26.9) | 257 (25.8) | 0.548 | 167 (24.5) | 167 (24.5) | 1.000 |
 Male factor | 452 (40.0) | 420 (42.1) | 0.329 | 273 (40.0) | 273 (40.0) | 1.000 |
 Unexplained factor | 48 (4.2) | 46 (4.6) | 0.686 | 16 (2.3) | 16 (2.3) | 1.000 |
Multiple pregnancies | 216 (19.1) | 137 (13.7) | 0.001 | 106 (15.5) | 112 (16.4) | 0.658 |