Well I am in a toss up of which is the right and wronge. Logically I say a parent has the right to know Emotionally I can see how it can become a painful issue.
I would start off with telling your wife you are thinking about having the test done. Gauge her response. If she makes to much of a fuss or says what a waste and time and money it would be in a trying to convince you not to do this mannor. I would further consider actually doing the test.
