N/A, not available.
| Study | Location | Design | N (cases) | Male/female | Mean gestational days (SD) |
| RATSS | Stockholm, Sweden | National prospective twin cohort | 75 (20) | 46:29 | 247 (9) |
| ALSPAC | Bristol, UK | Case-control nested in prospective cohort | 50 (25) | 36:14 | 271 (21) |
| Seaver Autism Center | New York, USA | Hospital-based case-control | 18 (10) | 12:6 | 258 (21) |
| Autism Tooth Fairy Study | Texas, USA | Community-based case-control | 50 (25) | 25:25 | N/A |