Table I.
Characteristics of the study subjects by BMI category.
| Characteristic | All subjects | BMI categorya | |||
|---|---|---|---|---|---|
| Underweight (n = 222) | Normal (n = 3046) | Overweight (n = 660) | Obese (n = 38) | ||
| Age, years | |||||
| <25 | 1291 (32.6) | 103 (46.4) | 1047 (34.4) | 129 (19.6) | 12 (31.6) |
| 25–29 | 1356 (34.2) | 75 (33.8) | 1042 (34.2) | 228 (34.5) | 11 (28.9) |
| ≥30 | 1319 (33.2) | 44 (19.8) | 957 (31.4) | 303 (45.9) | 15 (39.5) |
| Mean (SD) | 28.5 (5.5) | 26.8 (4.9) | 28.2 (5.4) | 30.3 (5.7) | 28.7 (5.9) |
| Ethnicity | |||||
| Han | 3844 (96.9) | 216 (97.3) | 2953 (96.9) | 640 (97.0) | 35 (92.1) |
| Others | 122 (3.1) | 6 (2.7) | 93 (3.1) | 20 (3.0) | 3 (7.9) |
| Education | |||||
| High school and lower | 1122 (28.3) | 84 (37.8) | 828 (27.2) | 200 (30.3) | 10 (26.3) |
| Junior college | 1376 (34.7) | 79 (35.6) | 1067 (35.0) | 219 (33.2) | 11 (28.9) |
| Undergraduate and higher | 1468 (37.0) | 59 (26.6) | 1151 (37.8) | 241 (36.5) | 17 (44.8) |
| Marital status | |||||
| Unmarried | 2333 (58.8) | 163 (73.4) | 1853 (60.8) | 296 (44.8) | 21 (55.3) |
| Married | 1367 (34.5) | 45 (20.3) | 982 (32.2) | 323 (48.9) | 17 (44.7) |
| Divorced | 90 (2.7) | 4 (1.8) | 69 (2.3) | 17 (2.6) | 0 (0.0) |
| Living with partner | 176 (4.4) | 10 (4.5) | 142 (4.7) | 24 (3.7) | 0 (0.0) |
| Current smoking status | |||||
| Non-smoker | 2694 (67.9) | 136 (61.3) | 2100 (68.9) | 433 (65.6) | 25 (65.8) |
| Smoker | 1272 (32.1) | 86 (38.7) | 946 (31.1) | 227 (34.4) | 13 (34.2) |
| Season at semen examination | |||||
| Winter (Dec, Jan, Feb) | 5759 (19.2) | 325 (17.9) | 4446 (19.5) | 936 (18.5) | 52 (17.2) |
| Spring (Mar, Apr, May) | 7257 (24.2) | 331 (18.2) | 5623 (24.7) | 1234 (24.3) | 69 (22.9) |
| Summer (Jun, Jul, Aug) | 8309 (27.7) | 524 (28.9) | 6228 (27.4) | 1472 (29.0) | 85 (28.1) |
| Autumn (Sep, Oct, Nov) | 8624 (28.9) | 635 (35.0) | 6465 (28.4) | 1428 (28.2) | 96 (31.8) |
| Abstinence period, days | |||||
| 2–3 | 3108 (10.4) | 201 (11.1) | 2341 (10.3) | 519 (10.2) | 47 (15.6) |
| 4–5 | 12 035 (40.2) | 641 (35.3) | 8648 (38.0) | 2629 (37.9) | 117 (38.7) |
| 6–7 | 14 806 (49.4) | 973 (53.6) | 11 773 (51.7) | 1922 (51.9) | 138 (45.7) |
| Mean (SD) | 5.4 (1.3) | 5.4 (1.4) | 5.4 (1.3) | 5.4 (1.3) | 5.2 (1.4) |
| No. semen samples per subject | |||||
| 0–5 | 1537 (38.8) | 80 (36.0) | 1185 (38.9) | 257 (38.9) | 15 (39.5) |
| 6–10 | 1504 (37.9) | 77 (34.7) | 1171 (38.4) | 244 (37.0) | 12 (31.6) |
| >10 | 925 (23.3) | 65 (29.3) | 690 (22.7) | 159 (24.1) | 11 (28.9) |
Data are shown as number (percentage, %), if not specified.
aBMI was categorized using the WHO criteria: underweight (<18.5 kg/m2), normal weight (18.5–24.9 kg/m2), overweight (25–29.9 kg/m2) and obese (≥30 kg/m2).