| N (%) | |
| 1) Age group (years) | |
| <20 | 123 (5.8) |
| 20 - 29 | 1098 (51.8) |
| 30 - 39 | 782 (36.9) |
| 40+ | 117 (5.5) |
| Total | 2120 (100) |
| Range (14 to 50) | |
| Mean ± SD (29.1 ± 6.3) | |
| 2) Count of US exams for each study subject | |
| 1 | 1253 (59.6) |
| 2 | 503 (23.9) |
| 3 | 203 (9.7) |
| 4 | 83 (3.9) |
| 5 | 37 (1.8) |
| 6 | 15 (0.7) |
| 7 | 8 (0.4) |
| Total | 2102 (100) |
| 3) Gestational age (the earliest in case of repeated US exams) | |
| Early pregnancy (<8 weeks) | 5 (0.2) |
| First trimester (8 - 14 weeks) | 487 (23.2) |
| Second trimester | 1096 (52.1) |
| Third trimester | 514 (24.5) |
| Total | 2102 (100) |
| Range (6.4 - 43) | |
| Mean ± SD (21.7 ± 8.2) |