In the effect of suboptimal breastfeeding summary (which was pretty sparse, to be honest, particularly where methods were concerned) no mention was made what the adjustment was made for. Were the parents in both cohorts screened for ASD, themselves? If not, what's to rule out that, actually, more of the non-breastfeeding mothers had undiagnosed ASD, with the double effect that they might find breastfeeding more difficult than NT mothers as well as passing on genes predisposing to autism?
My youngest is 7.5. He has severe autism. He breastfed for 29 months. Exclusively for the first 8. My eldest is 10, with autism and ADHD. He self weaned at 18 months, after several months of waning interest. He found it hard to tolerate the prolonged contact involved. If we hadn't already taken steps to ensure more future siblings, I have no idea what you would expect me to do to prevent them from having autism, wombles.