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Table 1 Baseline characteristics of immediate and delayed FET groups in the entire and propensity score-matched cohorts

From: Effects of immediate versus delayed frozen embryo transfer in high responder patients undergoing freeze-all cycles

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
  1. 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 (%)
  2. aImmediate FET and bDelayed FET means FET took place either within the first menstrual cycle following oocyte retrieval or afterwards
  3. *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