There are two types of chromosonal abnormality - some are pure chance - something wrong with that particular sperm or egg, or as the embryo cells split something goes wrong with the DNA. In that case there is every likelihood that next time it will all be fine. The second thing is that one or both of you might be carrying a dodgy gene that you are passing on, particularly if it is a recessive gene where you each have one normal copy so are fine, but if you each passed the abnormal copy to a baby it would not be viable. In that case there would be a chance that it could happen again. You need to ask for more details about what problem was identified and whether it could be passed on genetically or if it's just one of those things, but I would think that's what blood tests on each of you would be looking for.