Table 1.
Characteristics of the study subjects
| All subjects (N = 64,141) | |
|---|---|
| Sex of infants | |
| Boy | 32,727 (51.0%) |
| Girl | 31,414 (49.0%) |
| Gestational age at birth, mean [SD], weeks | 39.1 [1.1] |
| Birth weight, g | |
| < 2000 | 115 (0.2%) |
| 2000–2499 | 3268 (5.1%) |
| 2500–3999 | 60,186 (93.8%) |
| ≥ 4000 | 558 (0.9%) |
| Missing | 14 (0.0%) |
| Apgar score at 5 min | |
| 0–3 | 68 (0.1%) |
| 4–6 | 127 (0.2%) |
| ≥ 7 | 60,890 (94.9%) |
| Missing | 3056 (4.8%) |
| Delivery method | |
| Vaginal | 52,974 (82.6%) |
| Caesarean section | 11,022 (17.2%) |
| Missing | 145 (0.2%) |
| Maternal age at birth, mean [SD], years | 31.3 [4.9] |
| < 20 | 368 (0.6%) |
| 20–24 | 5002 (7.8%) |
| 25–34 | 41,294 (64.4%) |
| 35–39 | 14,617 (22.8%) |
| ≥ 40 | 2857 (4.5%) |
| Missing | 3 (0.0%) |
| Number of siblings | |
| 0 | 29,565 (46.1%) |
| 1 | 23,509 (36.7%) |
| ≥ 2 | 10,756 (16.8%) |
| Missing | 311 (0.5%) |
| Number of surgical procedures under general anesthesia | |
| 0 | 63,234 (98.6%) |
| 1 | 746 (1.2%) |
| 2 | 90 (0.1%) |
| ≥ 3 | 71 (0.1%) |
| Congenital disease at age 1 | |
| Head and face | |
| Yes | 217 (0.3%) |
| No | 63,924 (99.7%) |
| Eye and ear | |
| Yes | 506 (0.8%) |
| No | 63,635 (99.2%) |
| Spinal cord | |
| Yes | 52 (0.1%) |
| No | 64,089 (99.9%) |
| Heart | |
| Yes | 865 (1.3%) |
| No | 63,276 (98.7%) |
| Chest (without heart) and digestive organs (abdomen) | |
| Yes | 339 (0.5%) |
| No | 63,802 (99.5%) |
| Skin | |
| Yes | 1378 (2.1%) |
| No | 62,763 (97.9%) |
| Upper and lower limb/muscle/bone/joint | |
| Yes | 412 (0.6%) |
| No | 63,729 (99.4%) |
| Kidney/urogenital apparatus | |
| Yes | 562 (0.9%) |
| No | 63,579 (99.1%) |
| Endocrine system/hormone | |
| Yes | 130 (0.2%) |
| No | 64,011 (99.8%) |
| Metabolism | |
| Yes | 20 (0.0%) |
| No | 64,121 (100.0%) |
| Others | |
| Yes | 229 (0.4%) |
| No | 63,912 (99.6%) |
Data are n (%) unless otherwise specified
SD standard deviation