Narrowly versus broadly defined autism spectrum disorders: differences in pre- and perinatal risk factors.

This study examined the differential contribution of pre- and perinatal risks in narrowly versus broadly defined autism spectrum disorder (ASD) and across core symptom domains, IQ and co-morbid problems. Children with a DSM-IV diagnosis of autistic disorder (AD) (n = 121) or pervasive developmental disorder not otherwise specified (PDD-NOS) (n = 75) were compared to a typical control sample (n = 311). Diagnoses were based on extensive assessments between 12 and 49 months of age (M = 33.3, SD = 6.4) and re-evaluated at 43-98 months (M = 68.1, SD = 10.7) in 70% of the cases. Compared with controls, cases with ASD were more likely to be firstborn and show a suboptimal condition after birth. Case mothers reported more infections and more stress during pregnancy. Although the ASD subgroups showed mostly overlapping risks, cases with PDD-NOS differed from those with AD by higher exposure to smoking during pregnancy (SDP) and by a negative association of smoking with IQ, regardless of confounders. SDP appears to contribute more to broadly defined (PDD-NOS) than to narrowly defined ASD (AD). Findings suggest differences in etiological contributors between ASD phenotypes.

Head circumference and height abnormalities in autism revisited: the role of pre- and perinatal risk factors.

Pre/perinatal risk factors and body growth abnormalities have been studied frequently as early risk markers in autism spectrum disorder (ASD), yet their interrelatedness in ASD has received very little research attention. This is surprising, given that pre/perinatal risk factors can have a substantial impact on growth trajectories in the first years of life. We aimed to determine which pre/perinatal factors were more prevalent in ASD children and if these factors differentially influenced body growth in ASD and control children. A total of 96 ASD and 163 control children matched for gender participated. Data of growth of head size and body length during the first 13 months of life were collected. Data on pre/perinatal risk factors were retrospectively collected through standardized questionnaires. Results indicated that after matching for SES, prematurity/low birth weight and being first born were more prevalent in the ASD versus the control group. In addition, with increasing age children with ASD tended to have a proportionally smaller head circumference compared to their height. However, the effect of prematurity/low birth weight on head growth corrected for height was significantly different in ASD and control children: premature/low birth weight control children showed a disproportionate larger head circumference in relation to height during their first year of life, whereas this effect was absent in premature/low birth weight ASD children. This may suggest that the etiology of abnormal growth is potentially different in ASD and control children: where abnormal growth in control children is related to suboptimal conditions in the uterus, abnormal growth in ASD may be more strongly related to the causal factors that also increase the risk for ASD. However, prospective studies measuring growth and ASD characteristics in both premature/low birth weight and a terme children are necessary to support this conclusion.