Obstetric Risk Factors and Autism Spectrum Disorders in Finland

Background:  Current research suggests that obstetric risk factors occur more in ASD compared to unaffected siblings or matched controls. Although the findings are inconsistent, previous studies have reported associations between ASD and e.g. maternal hypertension or pre-eclampsia, uterine bleeding, threatened abortion, breech presentation, caesarean section and low Apgar scores. Most of these risk factors are likely to represent conditions related to fetal hypoxia. Previous population-based studies examining obstetric risk factors have usually included only cases with infantile/childhood autism or have used a broader definition of ASD. There are very few studies that have examined obstetric risk factors specifically for Asperger’s syndrome or PDD.   

Objectives: To examine the relationship between obstetric risk factors and childhood autism, Asperger’s syndrome and other pervasive developmental disorders (PDD).

Methods: Register-based case-control study from all singleton births in Finland from 1990-2005. A total of 4713 cases with diagnoses of childhood autism, Asperger’s syndrome or PDD (based on the ICD-10) were identified from the Finnish Hospital Discharge Register. Each case was matched to four controls on sex, date of birth, and place of birth. Information on obstetric risk factors was obtained from the Finnish Medical Birth Register. Conditional logistic regression models were used for statistical analyses.

Results: When adjusted with possible confounders childhood autism was associated with maternal high blood pressure (OR 1.45, 95% CI 1.0-2.0, P=.032), birth type by vacuum or forceps (OR 0.71, 95% CI 0.5-1.0, P=.043), Apgar scores less than 7 (OR 1.48, 95% CI 1.1-2.0, P=.018) and neonatal treatment with monitoring (OR 1.39, 95% CI 1.0-1.9, P=.045). PDD was associated with induced labour (OR 1.25 95% CI 1.1-1.5 P=.006), planned caesarean section (OR 1.34, 95% CI 1.1-1.7, P=.010), Apgar scores 7-8 (OR 1.22, 95% CI 1.1-1.4, P=.008) and NICU treatment (OR 1.45, 95% CI 1.1-1.9, P=.008), while Apgar scores less than 7 narrowly missed an association (OR 1.30, 95% CI 1.0-1.7, P=.060). Asperger’s syndrome was associated only with Apgar scores 7-8 (OR 1.19, 95% CI 1.0-1.4, P=.022).

Conclusions: Low Apgar scores as well as conditions requiring neonatal special follow-up were associated with childhood autism and PDD. These findings suggest that fetal distress is a potential risk factor for these disorders, but not for Asperger’s syndrome.