Obstetric risk factors and autism spectrum disorders in Finland.

OBJECTIVE: To examine the relationship between obstetric risk factors and childhood autism, Asperger syndrome, and other pervasive developmental disorders (PDDs). STUDY DESIGN: Registry-based case-control study from all singleton births in Finland from 1990-2005. Cases with childhood autism, Asperger syndrome, or PDD (n = 4713) were identified from the Finnish Hospital Discharge Register. Each case was matched to 4 controls on sex, date of birth, and place of birth. Information on obstetric risk factors was from the Finnish Medical Birth Register. Conditional logistic regression models were used for statistical analyses. RESULTS: When adjusted with confounders, childhood autism was associated with maternal high blood pressure (OR 1.49, 95% CI 1.1-2.1, P = .018), Apgar scores less than 7 (1 minute, OR 1.46, 95% CI 1.1-2.0, P = .021), and neonatal treatment with monitoring (OR 1.40, 95% CI 1.02-1.9, P = .038). PDD was associated with induced labor (OR 1.25 95% CI 1.1-1.5, P = .007), planned cesarean delivery (OR 1.34, 95% CI 1.1-1.7, P = .009), 1-minute Apgar scores 7-8 ( OR 1.22, 95% CI 1.1-1.4, P = .008) and less than 7 (OR 1.34, 95% CI 1.03-1.8, P = .032), and neonatal intensive care unit treatment (OR 1.52, 95% CI 1.2-2.0, P = .003). Asperger syndrome was associated only with 1-minute Apgar scores 7-8 (OR 1.19, 95% CI 1.03-1.4, P = .018). CONCLUSIONS: Low Apgar scores as well as conditions requiring neonatal special follow-up are important risk factors for childhood autism and PDD. These findings suggest that fetal distress is a potential risk factor for these disorders, but not for Asperger syndrome.

Risk of autism spectrum disorders in low birth weight and small for gestational age infants.

OBJECTIVE: To examine the relationship between birth weight, gestational age, small for gestational age (SGA), and 3 of the most common autism spectrum disorder (ASD) subtypes. STUDY DESIGN: In this population-based case-control study conducted in Finland, 4713 cases born between 1987 and 2005 with International Classification of Diseases-diagnoses of childhood autism, Asperger syndrome, or pervasive developmental disorder (PDD), were ascertained from the Finnish Hospital Discharge Register. Four controls, individually matched on sex, date of birth, and place of birth, were selected from the Finnish Medical Birth Register for each case. Conditional logistic regression models were used to assess whether birth weight and gestational age information predicted ASD after controlling for maternal age, parity, smoking during pregnancy, and psychiatric history, as well as for infant's major congenital anomalies. RESULTS: Very low (<1500 g) and moderately low (<2500 g) birth weight, very low gestational age (less than 32 weeks), and SGA increased risk of childhood autism (adjusted OR 3.05, 95% CI 1.4-6.5; 1.57, 1.1-2.3; 2.51, 1.3-5.0; and 1.72, 1.1-2.6, respectively). Very low and moderately low birth weight, very low gestational age, and SGA were also associated with increase in PDD risk (OR 3.44, 95% CI 1.9-6.3; 1.81, 1.4-2.4; 2.46, 1.4-2.3; and 2.24, 1.7-3.0, respectively). No associations were found between the perinatal characteristics and Asperger syndrome. The increased risks persisted after controlling for selected potential confounders. CONCLUSIONS: The finding that low birth weight, prematurity, and SGA were related to childhood autism and PDD but not to Asperger syndrome suggests that prenatal factors related to these exposures may differ for these ASD subtypes, which may have preventive implications.