Table 1 Characteristics of the patients and cycles
|  | Overall sample (n = 1897) | LH surge (n = 920) | Without LH surge (n = 977) | P |
|---|---|---|---|---|
Age (years) mean ± SD | 33.32 ± 4.62 | 33.07 ± 4.56 | 33.55 ± 4.67 | 0.258 |
 ≥ 37, n (%) | 446 (23.51%) | 198 (21.5%) | 248 (25.4%) | 0.584 |
BMI (kg/m2) mean ± SD | 21.42 ± 5.52 | 21.38 ± 2.76 | 21.55 ± 7.1 | 0.226 |
 18, n (%) | 156 (8.22%) | 75 (8.15%) | 81 (8.29%) |  |
 18 ≤  ~  < 24, n (%) | 1450 (76.43%) | 705 (76.63%) | 745 (76.26%) |  |
 24 ≤  ~  < 28, n (%) | 242 (12.75%) | 118 (12.83%) | 124 (12.69%) |  |
 ≥ 28, n (%) | 49 (2.6%) | 22 (2.39%) | 27 (2.76%) |  |
Infertility type, n (%) | Â | Â | Â | 0.781 |
 Primary | 1000 (52.71%) | 488 (53.1%) | 512 (52.4%) |  |
 Secondary | 897 (47.29%) | 432 (46.9%) | 465 (47.6%) |  |
Infertility cause, n (%) | Â | Â | Â | 0.663 |
 Tubal | 1252 (66%) | 618 (67.2%) | 634 (64.9%) |  |
 Decreased ovarian reserve | 74 (3.9%) | 36 (3.9%) | 38 (3.9%) |  |
 Endometriosis | 231 (12.18%) | 111 (12.1%) | 120 (12.3%) |  |
 Male factors | 279 (14.71%) | 118 (12.8%) | 161 (16.5%) |  |
 Others | 61 (3.21%) | 37 (4%) | 24 (2.4%) |  |
Infertility duration (years), median (range) | 2 (0–20) | 2 (0–20) | 3 (0–19) | 0.711 |
Antral follicle counts, mean ± SD | 6.19 ± 5.8 | 6.24 ± 5.85 | 6.13 ± 5.76 | 0.221 |
Basal hormone level, mean mean ± SD | ||||
 FSH (IU/L) | 5.15 ± 1.62 | 4.93 ± 1.20 | 5.73 ± 1.26 | 0.462 |
 LH (IU/L) | 5.24 ± 2.36 | 5.78 ± 1.99 | 4.21 ± 2.23 | 0.567 |
 E2 (pg/ml) | 36.98 ± 14.53 | 36.31 ± 11.40 | 38.63 ± 17.57 | 0.564 |
 Progesterone (ng/ml) | 0.28 ± 0.14 | 0.25 ± 0.11 | 0.32 ± 0.15 | 0.187 |
Hormone level, hCG day, mean ± SD | ||||
 FSH (IU/L) | 7.48 ± 3.96 | 10.06 ± 3.92 | 5.1 ± 1.94 |  < 0.001 |
 LH (IU/L) | 23.6 ± 14.44 | 35.08 ± 12.6 | 12.8 ± 3.85 |  < 0.001 |
 E2 (pg/ml) | 264.26 ± 92.93 | 257.99 ± 91.39 | 270.18 ± 94.02 | 0.909 |
 Progesterone (ng/ml) | 0.45 ± 0.23 | 0.59 ± 0.21 | 0.32 ± 0.16 |  < 0.001 |
Hormone level, FET day, mean ± SD | ||||
 E2 (pg/ml) | 115.1 ± 52.23 | 110.7 ± 47.73 | 119.07 ± 55.73 | 0.186 |
 Progesterone (ng/ml) | 18.33 ± 7.2 | 18.02 ± 6.93 | 18.61 ± 7.43 | 0.127 |
Endometrium thickness (mm) mean ± SD | 10.75 ± 2.08 | 10.8 ± 2.1 | 10.7 ± 2.1 | 0.283 |
 7, n (%) | 114 (6%) | 56 (6.09%) | 58 (5.94%) |  |
Fertilization type, n (%) | Â | Â | Â | 0.613 |
 IVF | 1275 (67.21%) | 621 (67.5%) | 654 (67%) |  |
 ICSI | 622 (32.79%) | 299 (32.5%) | 323 (33%) |  |
Cryopreservation time (day), mean ± SD | 72.73 ± 2.87 | 73.26 ± 2.59 | 72.47 ± 3.11 | 0.663 |
Number of embryo transferred, n (%) | Â | Â | Â | 0.282 |
 1 | 510 (26.88%) | 236 (25.65%) | 274 (28.05%) |  |
 2 | 1387 (73.12%) | 684 (74.35%) | 703 (71.95%) |  |
Embryo stage, n (%) | Â | Â | Â | 0.336 |
 Cleavage | 1585 (83.55%) | 758 (82.39%) | 827 (84.65%) |  |
 Blastocyst | 312 (16.45%) | 162 (17.61%) | 150 (15.35%) |  |
Embryo quality, good (%) | 96.3% | 96.5% | 96.2% | 0.236 |