How to research medical issues/concerns?

Greetings all, I had such good luck with a previous thread I wanted to ask another question. Since we currently have four children (8 and under), I don't know that we're at a good stage to have a special needs child. Obviously if we had another bio child we could have special needs but we're thinking we should try to avoid a special needs issue in adoption if we can. (Please forgive me those of you caring for special needs children if this sounds cold to the needs of those children). Do you fill out a form for an adoption stating what types of prenatal checks you want done? Do you ask for family history of the birth mom? Do you verify that the birthmom has received adequate checkups? I know you can't prevent everything and we need to understand that. Essentially, what are the best, most reasonable steps to take to try to ensure a healthy adoptive/adopted (?) child? Thank you