Motor delay - An early and more common "red flag" in girls rather than boys with autism spectrum disorder.

Background: Autism and intellectual disability may coincide and be preceded by global developmental delay or by motor delay.

Hypothesis: Motor delay in the context of global developmental delay is an initial "red flag" for ASD, with added risk in girls.

Objective: To assess early developmental milestones in girls with ASD as compared to diagnosed boys, considering prematurity risk.

Method: Developmental milestones in a cohort of 467 children with ASD - diagnosed at mean age of 3.4 years (SD = 2.2) - were analyzed according to gender and prematurity risk.

Results: 111 girls (24 %), 356 boys (76 %), presented with motor milestones acquisition grossly within the normal range. However, there was a shift towards acquisition of walking being at the later end of the norm range, with this shift being more prominent in girls. 60 % of girls and 47 % of boys with ASD had motor delay and 49 % of girls and 36 % of boys had global developmental delay. The extent of the delays was greater in the prematurity subgroup.

Conclusion: Global delay of early milestones occurred in half of children with ASD and in 60 % of girls with ASD. Delayed acquisition of independent walking is relatively more common in girls subsequently diagnosed with ASD.