Table 2.
Results of meta-analyses of studies examining selected prenatal, birth, and postnatal risk factors for attention-deficit/hyperactivity disorder (ADHD)
| Risk factor | Outcome Measure | Most common risk factor definition | ADHD Overall |
ADHD Diagnosis only |
|||
|---|---|---|---|---|---|---|---|
| Total sample size (number of studies) | Pooled effect size (95% CI)* | Total sample size (number of studies) | Pooled effect size (95% CI)* | ||||
| Prenatal risk factors | Pre-pregnancy weight | Dichotomous | Pre-pregnancy body mass index in the obese category (≥ 30 kg/m2) | 1,102,386 (9) | OR: 1.49(1.14; 1.94)** | ||
| Preeclampsia | Dichotomous | Preeclampsia | 972,772 (14) | OR: 1.26 (1.09; 1.46)** | 962,080 (13) | OR: 1.27 (1.10;1.47)** | |
| Pregnancy complications | Dichotomous | Placental abruption most common (others included) | 253,517 (12) | OR: 1.47(1.17; 1.86)** | 226,967 (10) | OR: 1.49 (1.16; 1.91)** | |
| Testosterone | Continuous | Finger length ratio (2nd digit (2D):4D ratio). A lower ratio represents greater testosterone exposure |
1,405 (9) | CC: −0.14 (−0.20; −0.09)** | 526 (3) | CC:−0.16 (−0.25; −0.08)** | |
| Risks occurring at birth | Perinatal asphyxia | Dichotomous | Perinatal asphyxia | 157,051 (8) | OR: 1.31 (0.99; 1.74) | 135,808 (7) | OR: 1.24 (0.92;1.66) |
| Labor complications | Dichotomous | Labor/delivery complications | 139,110 (6) | OR: 1.16(0.92; 1.48) | same as overall | ||
| Continuous | 1,122 (4) | CC: 0.01 (−0.08; 0.11) | |||||
| Mode of delivery | Dichotomous | Breech delivery, cesarean delivery, and vacuum delivery | 2,201,243 (24) | OR: 1.11 (0.99; 1.24) | 1,989,443 (18) | OR: 1.12 (0.98; 1.27) | |
| Breech delivery | Dichotomous | Breech delivery | 247,599 (6) | OR: 1.02 (0.78; 1.34) | 133,183 (3) | OR: 1.03 (0.76–1.41) | |
| Cesarean delivery | Dichotomous | Cesarean delivery | 2,123,517 (22) | OR: 1.12 (1.00; 1.25) | |||
| Vacuum delivery | Dichotomous | Vacuum delivery | 197,957 (5) | OR: 1.10(0.87; 1.39) | |||
| Postnatal risk factors | Apgar score | Dichotomous | Apgar score of <7 at 5 min | 8,189,263 (15) | OR: 1.30 (1.09; 1.54)** | 8,163,236 (13) | OR: 1.29 (1.08; 1.53)** |
| Neonatal illness | Dichotomous | Neonatal intensive care unit (NICU) admission | 166,891 (11) | OR: 1.50 (1.18; 1.92)** | 142,106 (10) | OR: 1.46 (1.14; 1.87)** | |
| Continuous | 913 (3) | CC: 0.11 (0.05; 0.18)** | |||||
| No breastfeeding | Dichotomous | Never breastfed | 13,229 (9) | OR: 1.55 (1.15; 2.10)** | |||
Note: all heterogeneity statistics were not significant and therefore are not reported
*
Odds ratio (OR) for dichotomous outcomes and correlation coefficient (CC) for continuous outcomes; completed via complete pooling. CI=confidence interval
**
Significant at p< 0.05