Table 1 Baseline characteristics of all transfer cycles
|  | Intact embryo group (n = 9846) | Blastomere loss group (n = 2259) | p value |
|---|---|---|---|
No. (%) | No. (%) | ||
History of reproduction | |||
 Age of oocyte retrieval, mean (SD), years | 31.12 (4.57) | 31.18 (4.05) | 0.515 |
 Age of embryo transfer, mean (SD), years | 31.64 (4.59) | 31.84 (4.13) | 0.046 |
 BMI, mean (SD), kg/m2 | 21.76 (3.00) | 21.68 (4.35) | 0.409 |
 Duration of infertility, mean (SD), years | 4.31 (2.91) | 4.42 (3.00) | 0.114 |
 Pluriparous | 731 (7.4) | 176 (7.8) | 0.550 |
 Primary infertility | 5048 (51.3) | 1265 (56.0) | < 0.001 |
Causes of infertility | |||
  Tubal infertility | 5265 (53.5) | 1234 (54.6) | 0.188 |
  Anovulatory | 205 (2.1) | 56 (2.5) | |
  Endometriosis | 201 (2.0) | 57 (2.5) | |
  Male-factor infertility | 1721 (17.5) | 365 (16.2) | |
  Unexplained infertility | 330 (3.4) | 63 (2.8) | |
  Combined a | 2124 (21.6) | 484 (21.4) | |
Characteristics of FET cycle | |||
 Type of embryo cryopreservation |  |  |  |
  Slowing freezing | 3986 (40.5) | 1793 (79.4) | < 0.001 |
  Vitrification | 5860 (59.5) | 466 (20.6) | |
 Type of FET cycle | |||
  Natural | 5085 (51.7) | 1255 (55.6) | 0.004 |
  HRT | 3063 (31.1) | 654 (28.6) | |
  OS | 1698 (17.3) | 359 (15.9) | |
 Numbers of embryo transferred | |||
  1 | 803 (8.2) | 320 (14.2) | < 0.001 |
  2 | 6679 (67.8) | 1015 (44.9) | |
  3 | 2364 (24.0) | 924 (40.9) | |