Table 1.

Classification into five domains of potential risk factors for ASD

Geographical region of maternal birth	Maternal country of birth, studied by geographical region of birth Categorized according to United Nations definitions (available at https://unstats.un.org/unsd/methodology/m49): Eastern Africa, Northern Africa, South/Eastern Asia, Western Asia, and Northern Europe
Other prenatal risk factorsa	a. Advanced parental age (parental aged ≥ 40) b. Parity (first or ≥ fourth) c. Clustering of pregnancy complications, including maternal health problems, such as gestational diabetes, preeclampsia, abnormal thyroid function, infections, and mental health problem; and maternal prenatal medication, such as antibiotics
Perinatal risk factorsb	a. Clustering of birth complications, such as intrauterine hypoxia or birth asphyxia, including 5 min Apgar scores < 7; elective and emergency caesarean section; and assisted birth, including vacuum extraction and forceps b. Preterm birth, gestational age ≤ 36 weeks c. Small size for gestational age (SGA), > 2 SD below the mean birth weight for the gestational age according to Swedish birth weight standards d. Other medical conditions during the neonatal period, such as infections and neonatal jaundice
Neurodevelopmental disorders in the family	A positive family history was defined as a child having a first or second degree relative (full siblings, parents, grandparents, aunts, uncles) affected by: a. ASD b. Other neurodevelopmental disorders, such as language disorder, ADHD, and epilepsy
Genetic findings/syndromes	a. In SNP array potentials causative copy number variations b. Medical syndrome suspected/Minor physical anomalies (MPA) c. Consanguinity

^aPrenatal period defined as the period of gestation

^bPerinatal period defined as the period immediately before and after the birth and to 4 weeks after birth