Table 1 Comparison of baseline and reproductive characteristics of the difference between primary and secondary infertile groups
|  | Primary infertility (N = 4378) | Secondary infertility (N = 3265) | P value |
|---|---|---|---|
Age at time of study (years) | 28.00 (26.00, 31.00) | 34.00 (30.00, 38.00) | < 0.001*** |
BMI at time of study (kg/m^2) | 22.56 (20.44, 25.36) | 23.59 (21.48, 25.98) | < 0.001*** |
Age at menarche (years) | 14.00 (13.00, 15.00) | 14.00 (13.00, 15.00) | < 0.001*** |
AAM category n (%) | |||
 ≤12 | 658 (15.0) | 351 (10.8) | < 0.001*** |
 13 | 1105 (25.2) | 734 (22.5) |  |
 14 | 1203 (27.5) | 889 (27.2) |  |
 15 | 794 (18.1) | 661 (20.2) |  |
 16 | 439 (10.0) | 397 (12.2) |  |
 ≥ 17 | 179 (4.1) | 233 (7.1) |  |
Educational level n (%) | Â | Â | Â |
 Primary school and below | 171 (3.9) | 247 (7.6) | < 0.001*** |
 Middle school | 1402 (32.0) | 1293 (39.6) |  |
 High school or technical secondary school | 949 (21.7) | 724 (22.2) |  |
 Junior college degree | 905 (20.7) | 423 (13.0) |  |
 Bachelor’s degree | 775 (17.7) | 530 (16.2) |  |
 Master’s degree and above | 176 (4.0) | 48 (1.5) |  |
Irregular menstruation n (%) | |||
 No | 3402 (77.7) | 2763 (84.6) | < 0.001*** |
 Yes | 976 (22.3) | 502 (15.4) |  |
Dysmenorrhea n (%) | Â | Â | Â |
 No | 3751 (85.7) | 2951 (90.4) | < 0.001*** |
 Yes | 627 (14.3) | 314 (9.6) |  |
Family history (Whether mother had infertility) n (%) | |||
 No | 4304 (98.3) | 3220 (98.7) | 0.276 |
 Yes | 74 (1.7) | 45 (1.3) |  |
Cause of infertility n (%) | Â | Â | Â |
 PCOS | 486 (11.1) | 149 (4.6) | < 0.001*** |
 Endometriosis | 90 (2.1) | 61 (1.9) |  |
 DOR | 99 (2.3) | 76 (2.3) |  |
 Unexplained infertility | 190 (4.3) | 113 (3.5) |  |
 Tubal factor | 3513 (80.2) | 2866 (87.8) |  |