Surely I Could Have Prevented This?
The certian answer is NO, you could not of prevented this. Be assured that there was nothing that you did while pregnant or even before pregnancy that would have caused or contributed to your child having this disease. Hirschsprung's is a genetic disease. To be technical, it is caused by a fault in the Ret proto-oncogene. In a number of cases this faulty gene is hereditary but in the most common form of Hirschsprung's there seems to be no family history. Why this gene is faulty is the subject of a lot of research but nothing points to it being environmental and therefore caused by the parent.
You can have genetic counselling to try to determine the risk of you having other children with HD. Once you have an HD child the risk of having another is increased but most parents go on to have other healthy children. So far there is no test that can be performed to show whether your unborn child has Hirschsprung's or not.
If you have a child with HD then the odds of having another are about 4%, depending on whether the new baby is a boy or girl and whether your HD child has long or short segment. Therefore, the odds of having a healthy child next is extremely good.