Autism Risk Associated with Parents’ Age and Educational Status?

Background: Advanced parental age has attracted attention as a potential risk factor for Autism spectrum disorder (ASD), since the beginning of this trend of delayed reproduction. Studies have reported increased risk of ASD when both parents are of older ages, when there are older fathers but not older mothers and vice versa, or neither. According to National Portugal Statistic, mean age of mother at birth, in 2010, was 28.6 years, reflecting a two years delay in motherhood compared to 2000. In 2014, it stood in 31.5 years. Increased prevalence of ASD is a phenomenon without complete explanation. Examining effects of interactions of parental age on ASD risk is important and if it represents independent risk factors. Moreover, the association between parental educational status and ASD is poorly understood.

Objectives:  To characterize the role of advanced parental age at birth in ASD comparing with a group of other neurodevelopmental disorders (OND) without ASD.

Methods:  Participantsincluded 1973 children and adolescents, ranging in age from 2 to 18 years old. They were divided into two clinical main groups: ASD (N=1202; Male/Female ratio – 5/1) versus OND (N=771; Male/Female ratio – 2.5/1). Participants were seen as part of an outpatient clinic in a tertiary Pediatric Hospital between 1995 and 2015. To be included, all participants had to have registered both parental date of birth; ASD was diagnosed according to positive score for both ADI-R and ADOS, and fulfilment of DSM-5 criteria. Parents of OND group completed the Social Communication Questionnaire to exclude comorbidity with ASD. Parental age was categorized into: < 25; 25 – 29; 30 – 34 and ≥ 35 years of age. To enhance comparability covariates were included: gender; parental educational status categorized according to International Standard Classification of Education – ISCED; birth order; gestational age; Apgar score and pregnancy complications. All statistical computations were performed resorting to IBM SPSS Statistics version 23. We considered the significance level (α) = 0.05

Results: Mean age of mothers at the time of birth was 30.8 ± 5.2 years for ASD and 29.8 ± 5.7 for OND. Mean age of fathers was 33.2 ± 6.0 and 32.7 ± 6.4 years among ASD and OND group, respectively. Significant differences were found between maternal ages of children with ASD and children with OND, t(1533.486)= -3.927, p<0.001 but not between the corresponding paternal ages, t(1562.170)= -1.840, p=0.066.

In addition, a significant difference between the two groups was found for parental education (Mann-WhitneyU, p<0.001) for ASD group, median parental education was level 3 and for OND group was level 2. In ASD subjects 75% of all fathers and mothers had a level of education equal or less than 4 and 6, respectively; in OND group 75% of all fathers and mothers obtained lowest level of educational (level 3).

Conclusions: In a large sample comparing parental age and educational level of ASD versus OND population we can state that older maternal age at birth and higher parental education was independently associated with increased odds of ASD than other neurodevelopmental disorders.