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) | 0.455 | 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) | 0.431 | 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 | 0.056 | 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 | 0.000 | 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) | 64 (9.4) | 64 (9.4) | ||
| Number of embryo transfer | 0.000 | 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 | 0.000 | 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 |
Abbreviations: BMI, body mass index; COH, controlled ovarian hyperstimulation; FET, frozen embryo transfer; GnRH-a, gonadotrophin-releasing hormone agonist; GnRH-ant, gonadotrophin-releasing hormone antagonist; HRT, hormone replacement therapy; IVF, in vitro fertilization; ICSI, intracytoplasmic sperm injection. Data are presented as number (%)
aImmediate FET and bDelayed FET means FET took place either within the first menstrual cycle following oocyte retrieval or afterwards
*The predictors of propensity score matching were maternal age, BMI, insemination method, COH protocol, number of embryo transferred, embryo stage, top or good embryo transfer, and cause of infertility. The match tolerance was set to 0.000001. Categorical variables were compared with χ2 test. #P value of differences of different trigger drugs in GnRH-ant protocol