Table 2 Environmental risk factors studied in autism/autism spectrum disorder (ASD) in the scientific literature
Risk factors | Comments |
|---|---|
Thalidomide | Time of critical exposure: 20 to 24 days after conception |
Misoprostol | Time of critical exposure: first trimester, near sixth week after conception. Used for illegal abortion. |
Valproic acid | Time of critical exposure: first 3 to 4 weeks after conception. Neural tube defects, cardiac malformations, craniofacial malformation. |
Rubella infection | Time of critical exposure: infection during the first 8 weeks |
Chlorpyrifos | Pesticide used at home, school, community and farms |
Organochlorated pesticides | Dicofol and endosulfan exposure. First to eighth weeks. Correlation between maternal residence near agricultural pesticide exposure and autism. |
Prenatal, neonatal and perinatal factors | Advanced maternal and/or paternal age (mother > 35; father > 40); bleeding during pregnancy; forceps or vacuum delivery; prolonged labor; low birth weight (< 2500 g); respiratory distress syndrome; meconium aspiration syndrome; preterm birth at < 33 weeks; breech presentation; gestational age < 35 weeks; mothers who used medicine during pregnancy |
Maternal immigration/mother born abroad | Increased risk of ASD according to region and ethnicity; more risk in Caribbean and African-American populations |
Daily smoking in early pregnancy | The risk of autism is associated with daily smoking in early pregnancy |
β2-Adrenergic receptor agonist | Used to treat premature labor. Continuous terbutaline exposure for 2 weeks had increased risk for ASD. |
Birth defects | Associated with a near twofold increased risk for autism overall |
Chlorinated solvents and heavy metals | Association between autism and estimated concentrations in ambient air around birth residence. Increased risk for solvent and metals (mercury, cadmium, nickel, trichloroethylene and vinyl chloride). |
Parental psychiatric history | Parental psychopathology is associated with risk of autism and effective disorders |
Alcohol and drugs | It is very unlikely that there is a strong association between prenatal alcohol exposure and autism |
High parental education | Families with higher education background will seek services, thus reporting a child with autism |
Lack of omega 3 fatty acids | Studies showed link between childhood development disorders and omega-6, omega-3 imbalances |
Congenital cytomegalovirus (CMV) infection | Timing of injury to the developing brain by CMV may be in the third trimester in some patients with ASD |
Singleton and concordant multiple births | Results indicated that ASD-concordant multiple births in boys tended to be higher than expected in March, May and September, but were 87% less in December, as compared with January |
Maternal autoimmune disorders | Maternal autoimmune disorders in women around the time of pregnancy are unlikely to contribute significantly to risk of autism (case-control study) |
Fetal alcohol syndrome (FAS) (case report) | Autistic behavior has not been previously associated with FAS. No statistical data, however it raises awareness that FAS could be a risk factor that should be evaluated by physicians. |
Neonatal hyperbilirubinemia | Not a risk factor associated with ASD. Children with any degree of bilirubin level elevation were not at increased risk of ASD. |
Antenatal ultrasound | Antenatal ultrasound is unlikely to increase the risk of ASD (case-control study) |
Ammonium perchlorate | No reports of risk found |
Mercury (vaccines) | No risk found |
Measles, mumps, rubella (MMR) vaccination | No evidence that supports MMR vaccination relationship with autism |