This is a common question in any family with someone diagnosed with autism. The strongest causal evidence points to genetics playing a role and children with a sibling with autism are more likely to have autism than children who don't have a sibling with autism. The actual percentage chance is unknown at this point. I can tell you that, in the vast majority of cases, the sibling doesn't end up with an autism diagnosis and I've worked with many many families for which only a single child has autism.
Hi hun. I empathize with this fear as I experienced it myself. I got pregnant with my last child when my oldest son was 7. We dealt with severe autism with my oldest but he is now fully integrated.
My youngest is neurotypical and shows no signs of autism.