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Table 2 Environmental risk factors studied in autism/autism spectrum disorder (ASD) in the scientific literature

From: Prenatal exposure of a girl with autism spectrum disorder to 'horsetail' (Equisetum arvense) herbal remedy and alcohol: a case report

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