Table 1.

Possible environmental risk factors for Autism Spectrum Disorder (ASD).

Risk Factor	Hypothesized Period of Action	Selected Studies
Advanced parental age	Conception	Durkin et al., 2008 [23]; Ben Itzchak et al., 2011 [24]; Geier et al., 2016 [25]; Sandin et al., 2016 [27]; Modabbernia et al., 2017 [26]
Use of hormonal induction; Assisted Reproductive Technologies (ART)	Conception	Auyeung et al., 2009 [36]; Zachor & Ben Itzchak., 2011 [38]; Liu et al., 2017 [31]
Environmental chemicals and toxicants: air pollution pesticides phthalates	Conception, prenatal	Volk et al., 2011 [69]; Becerra et al., 2013 [70]; Rossignol et al., 2014 [40]; Weisskopf et al., 2015 [67]; Gong et al., 2017 [71]; Raz et al., 2018 [73]; Eskenazi et al., 2007 [79]; Cheslack-Postava, 2013 [77]; Shin et al., 2018 [134]; Braun et al., 2014 [78]
Nutritional factors: maternal obesity or undernutrition folates vitamin D deficiency iron deficiency	Conception; prenatal; early postnatal	Georgieff et al., 2007 [45]; Krakowiak et al., 2012 [41]; Getz et al., 2016 [42]; Andersen et al., 2018 [43]; Schmidt et al., 2011, 2012 and 2017 [46,135,136]; Vinkhuyzen et al., 2017 [101]; Schmidt et al., 2014 [53]
Medications: valproate other AEDs SSRIs antibiotics antibiotic	Prenatal	Roullet, et al., 2013 [86]; Veroniki et al., 2017 [87]; Mezzacappa et al., 2017 [57]; Atladottir, 2012 [91]
Infections; Fever; Maternal Immune Activation (MIA)	Prenatal	Zerbo et al., 2013 [105]; Jiang et al., 2016 [137]; Brucato et al., 2017 [106]; Zerbo et al., 2013 [105]; Parker-Athill et al., 2010 [109]; Jones et al., 2017 [110]
Maternal individual factors and diseases: gestational diabetes; maternal melatonin levels; depression (?)	Prenatal	Gardener at al., 2009 [114]; Lyall et al., 2012 [115]; Jin et al., 2018 [120]
Delivery method	Perinatal	Dodds et al., 2011 [122]; Emberti Gialloreti et al., 2014 [123]
Fetal distress	Perinatal	Modabbernia et al., 2017 [26]; Wang et al., 2017 [126]