Objective To examine the relationship between birth weight, gestational age, small for gestational age (SGA), and three 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 ICD-diagnoses of childhood autism, Asperger syndrome or 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 (<1500g) and moderately low (<2500g) 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.

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Background Results of previous population-based studies examining associations between smoking during pregnancy and autism spectrum disorders (ASD) are contradictory. Furthermore, there is a lack of population-based studies examining the relationship between smoking during pregnancy and the main diagnostic subtypes of ASD. Methods We conducted a population-based nested case-control study based on the Finnish Prenatal Study of Autism (FIPS-A) among live-born infants delivered in Finland between 1987-05. Data on maternal smoking during pregnancy was available from the Finnish Medical Birth Register (FMBR) since October 1990. Data on ASD in the offspring was obtained from the Finnish Hospital Discharge Register (FHDR). Results Among the three subtypes of ASD, maternal smoking during the whole pregnancy was associated with an increased risk of pervasive developmental disorder (PDD) (odds ratio 1.2, 95% confidence interval 1.0, 1.5). The increase in odds persisted after controlling for maternal age, mother’s socioeconomic and psychiatric status, and infant’s weight for gestational age. However, smoking exposure limited to the first trimester was not associated with PDD or any of the other ASD subtypes. Conclusions Maternal smoking is related to a modest increase in risk of PDD, while no associations were observed for childhood autism and Asperger’s syndrome.

Aim of the study was to examine the associations between parental age and autism spectrum disorders (ASD). Data were based on the FIPS-A (Finnish Prenatal Study of Autism and Autism Spectrum Disorders), a case-control study with a total of 4,713 cases with childhood autism (n = 1,132), Asperger's syndrome (n = 1,785) or other pervasive developmental disorder (PDD) (n = 1,796), which were ascertained from the Finnish Hospital Discharge Register. Controls were selected from the Finnish Medical Birth Register. Conditional logistic regression models were used for statistical analyses. Advanced paternal age (35-49 years) was associated with childhood autism in offspring, whereas advanced maternal age was associated with both Asperger's syndrome and PDD in offspring (35 years or more and 40 years or more, respectively). Teenage motherhood (19 years or less) was associated with PDD in offspring. The main finding was that maternal and paternal ages were differentially associated with ASD subtypes. In addition to advanced parental age, teenage pregnancy seems to incur a risk for PDD in offspring.

This article presents an overview of the Finnish Prenatal Study of Autism and Autism Spectrum Disorders (FIPS-A), a new study designed to examine the relationship between prenatal serologic factors, mediating and moderating developmental antecedents, and risk of autism spectrum disorders (ASD). The FIPS-A is based on register linkages between births from 1987 to 2005 ascertained from the Finnish Medical Birth Register (FMBR) and other national registers on treatment for this group of disorders. All subjects were members of the Finnish Maternity Cohort (FMC), which consists of virtually all births in Finland from 1983 to the present, and which includes archived maternal serum samples. This study also capitalizes on other registry information, such as systematically collected data on pregnancy, prenatal and neonatal complications and manual data collection from well-child clinics providing developmental data from birth to the age of 7 years. In this paper, we describe the methods used in the FIPS-A study, including a description of the national registers, available data and case ascertainment procedures. Finally, we discuss implications of the data for future work on uncovering putative aetiologies of ASD and key strengths and limitations of the design.