Three possibilities:
1. Mixed up in hospital
2. Your wife slept with someone else
3. Chimerism

Use DNA testing. Check if

1. Child is [your confirmed child/related to you/not related to you]
2. Child is [confirmed child of wife/related to wife/not related to wife]

Depending on the combination, the result might be good/bad for you/wife

To check for chimerism also requires taking DNA from multiple parts of your body/wife's body.

This post has been edited by godhpf: Oct 6 2015, 04:36 PM