Table 1 Patient baseline demographics, cycle characteristics and cycle outcomes of the three groups according to the number of total in vitro fertilization cycles
Variable | Overall | 2 cycles | 3 cycles | ≥ 4 cycles | P value |
|---|---|---|---|---|---|
Baseline demographics | |||||
 No. of cases (cycles) | 203 (524 cycles) | 125 (250 cycles) | 52 (156 cycles) | 26 (118 cycles) |  |
 Age (years) | 34.3 ± 4.7 | 33.7 ± 4.4 a | 33.7 ± 4.9 b | 36.3 ± 4.4 ab | < 0.001 |
 Mean interval from 1st to last IVF cycle (months) | 19.1 ± 15.5 | 14.2 ± 14.2 ab | 24.7 ± 13.5 a | 31.3 ± 15.0 b | < 0.001 |
 BMI (kg/m2) | 21.5 ± 2.8 | 21.7 ± 3.1 | 21.2 ± 2.3 | 21.5 ± 2.7 | 0.220 |
 Infertility factors |  |  |  |  | 0.003 |
 Male factor | 194 (34 %) | 86 (33 %) | 58 (35 %) | 50 (38 %) | |
 Tubal factor | 119 (21 %) | 59 (22 %) | 42 (25 %) | 18 (14 %) | |
 Ovulatory factor | 75 (13 %) | 37 (14 %) | 15 (9 %) | 23 (18 %) | |
 Endometriosis factor | 87 (15 %) | 32 (12 %) | 37 (22 %) | 18 (14 %) | |
 Unexplained factor | 89 (16 %) | 51 (19 %) | 16 (9 %) | 22 (17 %) | |
Cycle characteristics | |||||
 IVF protocol |  |  |  |  | < 0.001 |
 GnRHa long protocol | 351 (67 %) | 179 (72 %) | 116 (74 %) | 56 (48 %) | |
 GnRHa short protocol | 130 (25 %) | 48 (19 %) | 31 (20 %) | 51 (43 %) | |
 Antagonist protocol | 38 (7 %) | 22 (9 %) | 6 (4 %) | 10 (9 %) | |
 ART method (n) |  |  |  |  | 0.132 |
 Conventional IVF | 336 (64 %) | 171 (68 %) | 92 (59 %) | 73 (62 %) | |
 ICSI | 188 (36 %) | 79 (32 %) | 64 (41 %) | 45 (38 %) | |
 Duration of stimulation (days) | 9.3 ± 1.8 | 9.4 ± 1.8 | 9.1 ± 1.7 | 9.4 ± 2.0 | 0.379 |
 No. of gonadotrophin ampoules used | 34.6 ± 14.5 | 32.5 ± 11.8 a | 33.3 ± 13.7 b | 40.8 ± 18.8 ab | < 0.001 |
 Estradiol (pg/mL) on hCG day | 2177.3 ± 1441 | 2377.4 ± 1541 a | 2360.5 ± 1443 b | 1505.4 ± 938 ab | < 0.001 |
 No. of follicles ≥ 16 mm on hCG day | 4.91 ± 3.1 | 5.25 ± 3.1 a | 5.23 ± 3.4 b | 3.77 ± 2.4 ab | < 0.001 |
 Number of oocytes retrieved | 6.9 ± 3.9 | 7.7 ± 4.0 a | 7.2 ± 3.9 b | 5.0 ± 3.1 ab | < 0.001 |
 EM (mm) on hCG day | 13.0 ± 3.1 | 13.0 ± 3.0 a | 13.5 ± 3.5 b | 12.3 ± 2.5 ab | 0.011 |
 Pre-ovulation serum progesterone (ng/mL) | 1.62 ± 0.6 | 1.72 ± 0.6 a | 1.62 ± 0.7 b | 1.41 ± 0.6 ab | < 0.001 |
 P/E2 ratio | 1.11 ± 1.2 | 1.13 ± 1.3 | 1.02 ± 1.1 | 1.19 ± 0.7 | 0.557 |
Cycle outcomes | |||||
 Normal fertilization rate (%) | 77.4 (2830/3655) | 77.1 (1488/1928) | 76.2 (865/1134) | 80.4 (477/593) | 0.778 |
 Mean no. of embryos transferred | 2.5 ± 1.0 | 2.5 ± 1.0 | 2.5 ± 1.1 | 2.3 ± 1.1 | 0.106 |
 Mean embryo score per embryo (Day 3) | 3.3 ± 1.0 | 3.4 ± 0.9 a | 3.3 ± 0.9 b | 3.0 ± 1.2 ab | 0.001 |
 Implantation rate (%) | 15.8 (208/1316) | 18.7 (120/642) a | 16.0 (64/399) b | 8.7 (24/275) ab | 0.004 |
 Clinical pregnancy rate / transfer cycle (%) | 33.7 (164/486) | 40.0 (94/235) a | 34.2 (50/146) b | 19.0 (20/105) ab | 0.022 |
 Live birth rate / transfer cycle (%) | 19.3 (94/486) | 25.1 (59/235) a | 18.4 (27/146) b | 7.6 (8/105) ab | 0.006 |