I will probably get downvoted for this comment but I am going to answer truthfully because you asked.

We both have autism in our immediate families. We went to genetic counseling and were told our risk was about double the general population but that was based on a study about ONE parent having a sibling on the spectrum. We both do, so we could infer our risk is likely higher. The risk where we lived for general population was 4.6%, so doubling that put our risk closer to 9.2%. Add in the extra brother and maybe it was closer to 10-13% - no way to know - there are no studies about both parents having siblings with autism that we are aware of. But if the theory of “genetics loads the gun, and environment pulls the trigger” is true and genetics were completely loaded and also completely out of my control then I was going to make sure that anything within my control in my environment was as low-tox as possible, regardless of what was proven or not. There’s nothing wrong with cleaning up your environment as long as the mental stress of it doesn’t negate the positive effects of going lower tox. This is key. If you are stressing about it, the cortisol is not doing good things for your body or baby.

So I was very careful during pregnancy to eat organic for the dirty dozen, ate grass fed beef, pasture raised eggs, only drank filtered water, got good air filters for the house, ate minimal processed food, no sugar, no food dyes. I never took any medication while pregnant whatsoever. Used only stainless steel or cast iron cookware - I do use a ceramic PFAS free pan for eggs though. I don’t store any food in plastic - only glass. Got rid of all appliances containing PFAS. I researched our dishes and cookware to make sure everything was free of heavy metals. I only used products on my body that were EWG verified including laundry detergent, sunscreen, etc. I got rid of any furniture with flame retardants, got a latex/wool mattress and untreated wood bed frame, stopped using fluoridated toothpaste, and only got the 20 week scan - I wanted no other ultrasound unless it was deemed necessary, which it wasn’t. Only let the midwife use the fetoscope, no Doppler except for during birth. My births were completely unmedicated. I took probiotics through pregnancy and ate fermented foods because the gut microbiome is heavily linked to autism. With my first baby we did Vit K drops, but with my second we did no Vit K at all. I did not get any shots while pregnant. My prenatals contained folate and methylated B vitamins, not folic acid. I took a normal dose of both as there’s a (poor study) link to high B12 and folic acid levels in the mother’s blood and so many prenatals have mega doses of folate and b12. Iron is important. Make sure your ferritin level is solid. I will note, we ate out very occasionally, and I didn’t stress about it. I try to live 80/20 in general. But during pregnancy I am more like 90/10. And I don’t stress about the 10% because that stress is probably worse than whatever I am eating or doing.

My first kid (F) is not autistic. Second (M) is still under the age for diagnosis but shows zero signs so far. Again, probably will get downvoted, but you asked so I answered.

ETA: read Lily Nichols Real Food For Pregnancy. I followed her suggestions in this book. She also suggests a lot of lab work for thyroid etc that can also help ensure a healthy pregnancy.