title: Caesarean section and risk of autism across gestational age: a multi-national cohort study of 5 million births.
abstract: The positive association between caesarean section (CS) and autism spectrum disorder (ASD) may be attributed to preterm delivery. However, due to lack of statistical power, no previous study thoroughly examined this association across gestational age. Moreover, most studies did not differentiate between emergency and planned CS.
  
  
  
  Using population-based registries of four Nordic countries and Western Australia, our study population included 4 987 390 singletons surviving their first year of life, which included 671 646 CS deliveries and 31 073 ASD children. We used logistic regression to estimate odds ratios (OR) and their 95% confidence intervals (CI) for CS, adjusted for gestational age, site, maternal age and birth year. Stratified analyses were conducted by both gestational age subgroups and by week of gestation. We compared emergency versus planned CS to investigate their potential difference in the risk of ASD.
  
  
  
  Compared with vaginal delivery, the overall adjusted OR for ASD in CS delivery was 1.26 (95% CI 1.22-1.30). Stratified ORs were 1.25 (1.15-1.37), 1.16 (1.09-1.23), 1.34 (1.28-1.40) and 1.17 (1.04-1.30) for subgroups of gestational weeks 26-36, 37-38, 39-41 and 42-44, respectively. CS was significantly associated with risk of ASD for each week of gestation, from week 36 to 42, consistently across study sites (OR ranged 1.16-1.38). There was no statistically significant difference between emergency and planned CS in the risk of ASD.
  
  
  
  Across the five countries, emergency or planned CS is consistently associated with a modest increased risk of ASD from gestational weeks 36 to 42 when compared with vaginal delivery.
authors.affiliation: Department of Medical Epidemiology and Biostatistics, Karolinska Institutet, Stockholm, Sweden.
authors.forename: Benjamin Hon Kei
authors.initials: BHK
authors.lastname: Yip
authors.affiliation: Telethon Kids Institute.|Centre for Child Health Research, University of Western Australia, Crawley, WA, Australia.
authors.forename: Helen
authors.initials: H
authors.lastname: Leonard
authors.affiliation: Department of Medical Epidemiology and Biostatistics, Karolinska Institutet, Stockholm, Sweden.|MRC Centre for Reproductive Health, University of Edinburgh Queen's Medical Research Institute, Edinburgh, UK.|Norwegian Institute of Public Health, Oslo, Norway.
authors.forename: Sarah
authors.initials: S
authors.lastname: Stock
authors.affiliation: Norwegian Institute of Public Health, Oslo, Norway.|Department of Global Public Health and Primary Care, University of Bergen, Bergen, Norway.
authors.forename: Camilla
authors.initials: C
authors.lastname: Stoltenberg
authors.affiliation: Telethon Kids Institute.|Centre for Child Health Research, University of Western Australia, Crawley, WA, Australia.
authors.forename: Richard W
authors.initials: RW
authors.lastname: Francis
authors.affiliation: National Institute for Health and Welfare, Helsinki, Finland.|Department of Child Psychiatry, Turku University and Turku University Hospital, Turku, Finland.
authors.forename: Mika
authors.initials: M
authors.lastname: Gissler
authors.affiliation: Department of Epidemiology and Preventive Medicine, Tel Aviv University, Tel Aviv, Israel.|Division of Psychiatry, Chaim Sheba Medical Center, Tel Hashomer, Israel.
authors.forename: Raz
authors.initials: R
authors.lastname: Gross
authors.affiliation: Department of Public Health, Institute of Epidemiology and Social Medicine, Aarhus University, Aarhus, Denmark.|Department of Economics and Business, National Centre for Register-based Research, Aarhus, Denmark.|Lundbeck Foundation Initiative for Integrative Psychiatric Research, Aarhus University, Aarhus, Denmark.
authors.forename: Diana
authors.initials: D
authors.lastname: Schendel
authors.affiliation: Department of Medical Epidemiology and Biostatistics, Karolinska Institutet, Stockholm, Sweden.|Department of Psychiatry, Icahn School of Medicine at Mount Sinai, New York, NY, USA and.
authors.forename: Sven
authors.initials: S
authors.lastname: Sandin
mesh_terms: D000293:Adolescent; D000328:Adult; D000067877:Autism Spectrum Disorder / Q000453:epidemiology*; D002585:Cesarean Section / Q000009:adverse effects*; D002648:Child; D015331:Cohort Studies; D004630:Emergencies; D005260:Female; D005865:Gestational Age; D006801:Humans; D007231:Infant, Newborn; D007391:International Cooperation; D016015:Logistic Models; D008297:Male; D011247:Pregnancy; D012042:Registries; D012537:Scandinavian and Nordic Countries / Q000453:epidemiology; D014904:Western Australia / Q000453:epidemiology; D055815:Young Adult
keywords: Autism; emergency caesarean section; epidemiology; gestational age; planned caesarean section; population based