Abstract
Guy et al published a screening study of children born preterm using the Modified Checklist for Autism in Toddlers (M-CHAT) questionnaire at age 2 years.1 This was one of the largest studies of preterms using the M-CHAT, and it included a follow-up telephone interview. Initially, the authors reported M-CHAT positivity in 14.5% of preterm children and 2.4% of true positives after the follow-up screens.
In our study, M-CHAT was part of a battery of three screening tests.2 We used a follow-up clinical evaluation with the Autism Diagnostic Observation Schedule instead of the recommended telephone interview; however, in our opinion, this substitution improved the accuracy of our results. Our initial M-CHAT positivity was 17.8% and positivity for the whole test battery was 35.7%.
After clinical examination, autism prevalence was 9.7%. The study by Guy et al had some similarities to our study, such as age of screening (2 years, age corrected), comparable rates of return of questionnaires in the preterm cohort (58% vs 63.6%), and similar M-CHAT positivity (14.5% vs 17.8%).
However, the prevalence of autism was discrepant between the studies (2.4% vs 9.7%). In our opinion, the most plausible explanation is that the use of a battery of three screening tests diminished the rate of false negative screening results.
Another reason for the difference may have been different inclusion criteria. Guy et al focused on moderate and late preterm children (32-36 weeks), and we included all preterm children with birth weights less than 1500 g.
An additional, although speculative, explanation could be that the follow-up telephone interview was overly restrictive with regard to M-CHAT positivity.