Late Prematurity and Birth History in Children with Autism

Background:   The prevalence of children with autism spectrum disorders (ASD) has increased over the past two decades. Major advances in the field of autism include early screening for children with ASD and those considered high risk for the disorder. Over this same time period, the number of infants born preterm has also increased, mostly among those classified as late preterm [LPT] (34-36 weeks gestation). These infants account for 70% of the preterm birth in the US. Vulnerability to a resulting neurobiologic issue, such as the development of ASD, by LPT infants is suspected but has not been well studied.

Objectives:   This study explored the relationship between late prematurity, birth history, and autism. The overall objective was to discern whether LPT infants carry the same risk for ASD as full term infants in a retrospective cohort analysis of patients from the Marcus Autism Center.

Methods:   With the aim of estimating the probability of autism in LPT children, a retrospective cohort analysis of 664 children was undertaken to look at gestational age, ASD, and birth history. In order to estimate the probability of autism in the LPT population, Bayes’ Rule was used. Three pieces of information were necessary to estimate this probability: (1) The overall probability of autism in all children (CDC); (2) Overall probability of the proportion of children born LPT (National Center for Health Statistics); (3) The proportion of late prematurity among autistic children. The first two pieces of information were treated as “population parameters” since this data is obtained from Published National Population Estimates. The third parameter was estimated from the 664 children from the Marcus database in this study.

Results:  Our sample of children included 664 patients: 498 were term, 47 were early preterm (EPT), 92 were LPT, and 27 infants were post-term. Of these 21% of the population was female and more than half identified themselves as a minority: African American (34.1%) or Other (19.8%).  There were 405 children diagnosed with an ASD in the sample as a whole. Consistent with the literature, our data revealed EPT children have nearly 2 times the risk of an ASD diagnosis when compared to Term Children (P <.05). Late Pre Term (LPT) children have 1.2 times higher risk of an ASD diagnosis when compared to Term Children – this was not statistically significant at p=0.05. However, when considering all children in sample who were referred for ASD testing ,the relative risk ratio is 1.6 times higher than Term children and this was statistically significant at p=0.05.

Conclusions:   There is a paucity of evidence regarding the neurodevelopmental outcomes of the LPT children during early school age years. At 35 weeks gestation, the infant’s overall brain weight is only 60% of term weight. Because of this anatomical and pathophysiological finding, it is extremely important that we improve our understanding of brain development in the last few weeks of gestation and identify risk factors that may lead to the development of ASD in the LPT infant.