It’s clear that genetics plays a major role in the aetiology of autistic spectrum disorder (ASD), but the genuine increase in prevalence over recent decades suggests that environmental factors are also responsible. If ASD is considered to be a neurodevelopmental disorder, rather than a social construct, then antenatal influences during early brain development may be important. Potential prenatal causes suggested thus far are many and varied, including paracetamol (Archivist Oct 2016 doi.org/10.1136/archdischild-2016–3 11 708), antidepressant drugs (Archivist March 2016 doi.org/10.1136/archdischild-2016–3 10 462), ultrasound (Archivist Sept 2018 doi.org/10.1136/archdischild-2018–3 15 816), season of conception (Lucina Dec 2016 doi.org/10.1136/archdischild-2016–3 12 102), and obesity, among many others.

Several studies have hinted at a link with maternal air …