Table 1. Sample Characteristics of Later-Born Siblings Based on Familial Risk Status.
| Characteristic | No Known Risk (n = 14 287) | ADHD Risk (n = 730) | ASD Risk (n = 158) |
|---|---|---|---|
| Child sex (% male) | 50.73 | 51.92 | 48.10 |
| Proband sex (% male)a | 50.21a | 74.66a | 83.54a |
| Gestational age, mean (SD), wk | 39.10 (4.05) | 39.20 (3.12) | 39.13 (5.61) |
| Maternal age at delivery, mean (SD), yb | 28.34 (29.53) | 29.04 (30.74) | 29.70 (19.10) |
Abbreviations: ADHD, attention-deficit/hyperactivity disorder; ASD, autism spectrum disorder.
a
All groups differ (P < .001).
b
ASD risk group differs from no-known-risk group and ADHD risk group (P < .001).