Table 1.
Description of the study populations’ pregnancy- and delivery-related characteristics
| Cases | Cohort controls | Matched controls | |||
|---|---|---|---|---|---|
| Birth characteristic | Perthes n (%) |
Not Perthes n (%) |
Not Perthes n (%) |
p-valuea, c | P-valueb,c |
| Diabetes during pregnancy | 0.781 | 0.310 | |||
| No | 1955 (98.4) | 2,096,467 (98.5) | 3923 (98.7) | ||
| Yes | 32 (1.6) | 32,657 (1.5) | 51 (1.3) | ||
| Hypertension (mother) | 0.769 | 0.460 | |||
| No | 1965 (98.9) | 2,104,036 (98.8) | 3921 (98.7) | ||
| Yes | 22 (1.1) | 25,088 (1.2) | 53 (1.3) | ||
| Vaginal delivery (breech) | 0.014 | 0.750 | |||
| No | 1841 (92.7) | 2,000,647 (94.0) | 3691 (92.9) | ||
| Yes | 146 (7.3) | 128,477 (6.0) | 283 (7.1) | ||
| Emergency cesarean section (breech) | 0.010 | 0.024 | |||
| No | 1956 (98.4) | 2,108,099 (99.0) | 3938 (99.1) | ||
| Yes | 31 (1.6) | 21,025 (1.0) | 36 (0.9) | ||
| Elective cesarean section (breech) | 0.092 | 0.229 | |||
| No | 1979 (99.6) | 2,124,355 (99.8) | 3965 (99.8) | ||
| Yes | 8 (0.4) | 4769 (0.2) | 9 (0.2) | ||
| Breech delivery | < 0.001 | 0.141 | |||
| No | 1802 (90.7) | 1,976,157 (92.8) | 3649 (9.8) | ||
| Yes | 185 (9.3) | 152,967 (7.2) | 325 (8.2) | ||
| Birthweight for gestational age | < 0.001 | 0.002 | |||
| Appropriate for gestational age | 1805 (90.8) | 1,990,865 (93.5) | 3698 (93.1) | ||
| Large for gestational age | 61 (3.1) | 61,161 (2.9) | 115 (2.9) | ||
| Small for gestational age | 121 (6.1) | 77,098 (3.6) | 161 (4.1) | ||
| Birthweight | < 0.001 | < 0.001 | |||
| Normal birthweight, ≥2500 g | 1865 (93.9) | 2,045,135 (96.1) | 3816 (96.0) | ||
| Low birthweight, 1500 g – 2499 g | 99 (5.0) | 74,789 (3.5) | 139 (3.5) | ||
| Very low birthweight, < 1500 g | 23 (1.2) | 9200 (0.4) | 19 (0.5) | ||
| Gestational age | < 0.001 | 0.002 | |||
| At term, 37–42 weeks | 1630 (82.0) | 1,818,175 (85.4) | 3380 (85.1) | ||
| Post term, > 42 weeks | 205 (10.3) | 196,834 (9.2) | 383 (9.6) | ||
| Preterm, 32–36 weeks | 135 (6.8) | 103,207 (4.8) | 194 (4.9) | ||
| Very preterm, < 32 weeks | 17 (0.9) | 10,908 (0.5) | 17 (0.4) | ||
| Apgar 5 | < 0.001 | 0.013 | |||
| > 7-max | 1908 (97.2) | 2,072,508 (98.2) | 3862 (98.2) | ||
| 0–7 | 55 (2.8) | 36,965 (1.8) | 71 (1.8) | ||
a cases vs population; b cases vs match controls; c Pearson’s chi-square