What the genetic counselor probably meant was that even though it appears to have been a sporadic event with DC1's problem, then can't say for sure. If they tested you and your DH to make sure you don't carry the something similar, then it's extremely unlikely you'd have another baby with it. The reason the risk wouldn't be zero is because there is a very small chance for gonadal aka germ-line mosacism. This means that all the cells in your body are normal, but there could be a mutation in what were the precursor cells to sperm or egg so that only egg or sperm would carry the mutation. So if they tested your blood and it was normal, they can't rule out that egg or sperm could carry the mutation. This is an extremely rare, though well documented, occurence. So odds are you are at low risk, but you can do PGD with any future pregnancies to be even more sure if you wanted. Since you are at a low risk though, getting pregnant naturally would probably be fine if you don't want to go through IVF/PGD and you could test as early as 10 wks with the CVS.