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The composition gestational weeks of each class and the number of images.
| Class | Gestational week | Number of images (%) |
| Class I (n = 3323) | 20 | 11 (0.3) |
| 21 | 97 (2.9) | |
| 22 | 712 (21.4) | |
| 23 | 1625 (48.9) | |
| 24 | 175 (5.3) | |
| 25 | 120 (3.6) | |
| 26 | 161 (4.9) | |
| 27 | 82 (2.5) | |
| 28 | 90 (2.7) | |
| 29 | 250 (7.5) | |
| Class II (n = 2142) | 30 | 549 (25.6) |
| 31 | 487 (22.7) | |
| 32 | 182 (8.5) | |
| 33 | 116 (5.4) | |
| 34 | 238 (11.1) | |
| 35 | 252 (11.8) | |
| 36 | 318 (14.9) | |
| Class III (n = 1548) | 37 | 365 (23.6) |
| 38 | 395 (25.5) | |
| 39 | 404 (26.1) | |
| 40 | 336 (21.7) | |
| 41 | 48 (3.1) |
