|
| Risk factors | Risk estimates |
|
| Pregnancy and birth |
| Male gender | Risk of schizophrenia OR 1.8 (95% CI 1.1–3.0) [3, 4] |
| Parental psychosis | Risk of schizophrenia HR 2.8 (95% CI 1.7–4.5) [5] |
| Maternal antenatal depression | Nonsignificant risk of schizophrenia RR 1.5 (95% CI 0.9–2.4) [6] |
| Unwantedness of a pregnancy | Risk of schizophrenia OR 2.4 (95% CI 1.2–4.8) [7] |
| High paternal social class at birth (females) | Risk of schizophrenia RR 2.4 (95% CI 1.2–4.9) [8] |
| Perinatal brain damage | Risk of schizophrenia OR 4.6 (95% CI 1.7–12.1) [3, 9] |
| Deviant intrauterine growth | Increased risk of schizophrenia for both low (OR 2.5; 95% CI 1.2–5.1) and high (OR 2.4; 95% CI 1.1–4.9) birth weight and for both low (OR 2.6; 95% CI 1.1–5.9) and high (OR 1.8; 95% CI 1.0–3.5) birth length [5, 9, 10] |
| Birth order | Risk of schizophrenia among male first-borns (observed-expected ratio 1.5; 95% CI 1.0–2.2) and nonsignificant risk among female last-borns (1.3; 95% CI 0.9–1.9) [11] |
| Grand multiparity, six or more | Nonsignificant risk of schizophrenia OR 1.1 (95% CI 0.6–2.1), significant risk of other psychosis OR 2.3 (95% CI 1.2–4.7) [12] |
|
| Childhood and adolescence |
| Use of vitamin D supplementation, at least 2000 IU | Decreased risk of schizophrenia RR range: 0.08–0.23 [13] |
| Markers of development in childhood | Risk of schizophrenia, later age of learning to stand (RR 1.5; 95% CI 1.0–2.2) and walk (RR 1.3; 95% CI 1.0–1.6) [14] |
| Family type (single-parent versus two-parent) at birth to 14 years | No significant differences [15] |
| Viral central nervous system infection before age 14 | Risk of schizophrenia OR 4.8 (95% CI 1.6–14.0) [3, 16] |
| Intelligence Quotient (IQ) <85 up to the age of 14 years | Risk of schizophrenia OR 4.8 (95% CI 2.2–10.3) [3] |
| Excellent school performance age 16 years (males) | Risk of schizophrenia OR 3.8 (95% CI 1.6–9.3) [17] |
| Lower school marks and below normal class age 16 years | Lower school marks associated with risk for nonpsychotic disorders, but not for schizophrenia or other psychoses. Below normal class associated with schizophrenia risk in boys OR 2.8 (95% CI 1.5–5.7) [18]. |
|
| Other premorbid factors |
| Severe injuries (e.g., fractures) before onset of psychosis | Risk of psychotic disorder, having a fracture HR 2.9 (95% CI 1.4–6.0) [19] |
| Seasonality | Rate of first admission for schizophrenia lower in spring compared to other seasons [20] |
| Paternal age | No significant risk by paternal age categories [21] |
|
| Interaction studies |
| Parental psychosis and maternal antenatal depression | Risk of schizophrenia highest in the offspring with both maternal depressed mood during pregnancy and parental psychosis (OR 9.4; 95% CI 4.2–20.9) [22] |
| Parental psychosis and early risk factors | Risk for schizophrenia highest among those with parental psychosis and biological risk factor: parental psychosis and high birth weight HR 7.9 (95% CI 1.8–34.8), parental psychosis and high birth length HR 4.3 (95% CI 1.1–16.2), parental psychosis and any biological risk HR 3.6 (95% CI 1.3–10.3), and parental psychosis and high maternal education HR 0.2 (95% CI 0.1–0.9) [5] |
|
| Associations between risk factors |
| Motor performance at age 1 and school performance at age 16 | Age of learning to stand associated with school mark of physical education in schizophrenia but not in controls [23] |
| Parental psychosis and advanced paternal age | Maternal schizophrenia associated with higher advanced paternal age [24] |
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