Table 3.
Risk of autism according to seasonality of conception and birth.
| Reference | Country/Year | Diagnosis | Case-Control Numbers | Case—Control Characteristics | Confounders/Covariates | Excess Conception | Excess Birth |
|---|---|---|---|---|---|---|---|
| [92] | Canada 1986 | DSM-III | 179-NR | Low functioning (IQ < 50) and high functioning (IQ > 50) autism, non-verbal and verbal autism from medical records from two different centres-live births | March vs. Sep-Feb | ||
| Spring-early summer vs. winter and autumn (Aggregated sample) | |||||||
| Spring vs. winter and autumn (Low functioning, nonverbal, male) | |||||||
| [91] | Japan 1988 | DSM-III | 80–71,013 | Native infantile autism <8 years from clinic outpatients-children <8 years from annual reports | Second quarter of the year (corresponding to spring) vs. first and third quarter* | ||
| [90] | Sweden 1990 | DSM-III-R | 100-NR | Cryptogenic autism-populations born in Sweden (Central Bureau of statistics) | Cases with medical conditions and of mothers immigrated to Sweden from non-European countries were excluded | March | |
| [89] | UK 1992 | ICD-9, DSM-III | 1435–196–121–24,957,169 | National autistic sample-clinic sample-sibling controls-live births | Significantly deviated from the general populations’ expected moth of birth (national sample) | ||
| December, January, June, July and October | |||||||
| [88] | Denmark 1994 | ICD-9 | 328-NR | Infantile autism-autism like disorder-borderline psychosis from clinic outpatients-live births | March and April vs. November December | ||
| [87] | Israel 1995 | DSM-III-R | 188–1,992,410 | Infantile autism-live births | March and August | ||
| [86] | International 1999 | DSM-IV, ICD-10 | 620–284 | Cases with autism from international multisite field trial for DSM-IV-Individuals with mental retardation from patients of a clinic | No association | ||
| [84] | Netherlands 2000 | ICD-9 | 1031-NR | National registry of mentally retarded patients with AD and PDD-NOS (IQ < 35)-general population birth data | No association (month and season) (Aggregated sample) | ||
| Second quarter of the year (Low functioning) | |||||||
| [85] | US 2000 | DSM-III-R | 175–123 | High and low functioning autism (verbal IQ cut off of 65) recruited for a research project-full siblings and half siblings | Arbitrary assignations of month to season | No association (aggregated sample) | |
| March (more low functioning and socially passive autism) (Boston subset) | |||||||
| [64] | Sweden 2002 | ICD-9 | 408–2040 | Infantile autism <10 years from medical birth register-birth register | Maternal age, parity, smoking, mother’s country of birth, hypertensive disease, diabetes, pregnancy bleeding, mode of delivery, gestational age, birth weight, Apgar score, congenital malformation | No association | |
| [83] | Israel 2006 | ICD-10 | 211–311,169 | ASD adolescents (age of 17) from military medical registry-live births | Year of birth, socioeconomic status | No association | |
| [77] | Denmark 2007 | ICD-10 | 1860–407,117 | ASD and ASD subcategories from psychiatric registry-live births | General trend for increase in incidence over time, follow up time, length of gestation | No association | No association |
| [82] | US 2008 | DSM-IV | 1051–1,458,011 | ASD singletons and multiple births from medical records-statistics data for singleton and multiple live births | Number of births and gender | Spring (April), summer (late July) and autumn (October) vs. winter (December and January) (Singletons and multiple births) | |
| [80] | Denmark 2010 | ICD-10 | 317–733,826 | Infantile autism from medical birth register-live births | Gender, maternal smoking status, irregular fetal presentation, birth weight, gestational age, Apgar score, parental age, maternal citizenship, congenital malformation | Winter (October to March) vs. Summer (April to September), 2.21 (1.24–3.94) vs. 1.02 (0.41–2.50) | |
| [81] | Egypt2010 | DSM-IV | 70–40 | ASD (recruited for the purpose of the study)-non ASD healthy controls | No significant difference | ||
| June (26.7%) followed by March and April (11.4%,) | |||||||
| [76] | UK 2010 | ICD-10 | 86–13,892 | ASD from medical and educational records-live births | Summer vs. winter 2.08 (1.18-3.70) | Spring vs. autumn (reference), 1.86 (1.01-3.37) | |
| [75] | US 2011 | ICD-9 | 19,328–6,585,737 | Full syndrome autism <6 years and live births <6 years from dataset | Gender, race/ethnicity, Preterm birth, maternal age, maternal education, maternal place of residence at childbirth and maternal year of conception | Winter (January, February and March) vs. Summer, 1.06 (1.02–1.10) | November vs. April (reference), 1.12 (1.05–1.20) |
| [74] | US 2012 | DSM-IV | 8,074–3,888,495 | AD not comorbid with mental retardation-live births | Gender, parental age and education, race and ethnicity, insurance status, preterm birth and low birth weight | Winter (the last 3 weeks of November and first week of December), 2.11, 1.72 and 1.53 in 1994, 1995 and 1996, respectively | |
| [79] | Turkey 2014 | DSM-IV | 54–54 | ASD (recruited for the purpose of the study)-non ASD healthy controls | No association | ||
| [78] | Sweden 2015 | DSM-IV-TR | 58–58 | ASD (recruited for the purpose of the study)-non ASD siblings | No association in children of Middle Eastern/African ethnicity | ||
| Spring vs. Summer, 38% vs. 10% in ASD and 18% vs. 35% in non ASD in children of Sweden and European ethnicity |