I think that if you're not ready to have a disabled child, you're not ready for a child at all.

That doesn't mean you wouldn't have a lot of learning to do if you did have a disabled child, or that you wouldn't be overwhelmed at first; it does mean that if you can't accept the possibility that your child may have a disability, then you probably shouldn't be having children. That's true whether or not you have an increased risk.

Any child may be born with a disability, or acquire one later on. Random genetic glitches, unavoidable accidents, and unpredictable illnesses may all leave a child with a disability. Most disabilities are not predictable; so when a person decides to have a child, they should be willing to take on all that parenting implies--including the possibility that their child may have a disability. If your idea is, "If this child has autism (or CP, or Down syndrome, or dyslexia, or any other disorder), I can't possibly be a parent," then you shouldn't be having a child.

You don't have to feel confident about being a perfect parent; it'd probably be weird if you were. But you shouldn't have a child until you can say, "We will love and raise this child--boy or girl, disabled or not, strong-willed or compliant; whoever they are, makes no difference, because we are going to be this child's parents and nothing can change that."