Table 2 ART procedures of pregnancies carried to delivery following FET with different endometrial preparation protocols
|  | NC (N = 1921) | OS (N = 360) | HRT (N = 1583) | p |
|---|---|---|---|---|
No. (%) | No. (%) | No. (%) | ||
Characteristics of oocytes retrieval cycle | ||||
 COH protocol | ||||
  GnRH-agonist regimen | 897 (46.69) | 181 (50.28) | 743 (46.94) | 0.345 |
  GnRH-antagonist regimen | 904 (47.06) | 166 (46.11) | 732 (46.24) |  |
  Microflare protocol | 100 (5.21) | 11 (3.06) | 85 (5.37) |  |
  Others | 20 (1.04) | 2 (0.56) | 23 (1.45) |  |
 Type of insemination | ||||
  IVF | 1276 (66.42) | 240 (66.67) | 1063 (67.15) | 0.901 |
  ICSI | 645 (33.58) | 120 (33.33) | 520 (32.85) |  |
 Number of oocytes retrieved | ||||
   ≤ 10 | 712 (37.06) | 123 (34.17) | 535 (33.80) | 0.171 |
  11–20 | 873 (45.45) | 161 (44.72) | 739 (46.68) |  |
   > 20 | 336 (17.49) | 76 (21.11) | 309 (19.52) |  |
Characteristics of FET cycle | ||||
 Day of embryo transfer | ||||
  Day3 | 1049 (73.35) | 258 (71.67) | 1140 (72.02) | 0.724 |
  Day4 | 299 (15.56) | 56 (15.56) | 267 (16.87) |  |
  Day5 | 213 (11.09) | 46 (12.78) | 176 (11.12) |  |
 Number of embryo transferred | ||||
  Single embryo transfer | 214 (11.14) | 33 (9.17) | 181 (11.43) | 0.811 |
  Multiple embryo transfer | 1707 (88.86) | 327 (90.83) | 1402 (88.57) |  |
 Hormone level before embryo transfer | ||||
  E2, Median [IQR], ×103 pmol/L | 1.20 [0.86–1.88] | 1.64 [1.01–2.69] | 1.86 [1.07–3.22] | < 0.001 |
  P4, Median [IQR], nmol/L | 2.90 [1.80–3.60] | 2.50 [1.50–2.60] | 1.50 [0.90–2.40] | < 0.001 |
  LH, Median [IQR], IU/L | 14.05 [9.20–24.90] | 10.60 [6.90–17.40] | 12.00 [7.50–20.30] | < 0.001 |
 Endometrial thickness, Mean ± SD, mm | 9.54 ± 1.46 | 9.52 ± 1.52 | 9.55 ± 1.43 | 0.952 |