Hey Mate,
Are you serious in getting a reply, so be it. Being a father is a Special thing, and firstly i congratulate you. The next thing is...
Its a family issue : You are the best person to judge on what to do, mine or anyone's advice shouldn't even bother you. I may get your point but do you really want a DNA test done with a 5 days old kid. I hope not, so let the time take its own course, She is still a 5 days old beautiful little princess. Let her be a healthy child in next two months. Until then, i guess your wife will talk to you or may be the child got exchanged at the hospital, so you can try talking to her and solve the problem
Man to Man : I know the thought of being cheated, poisons your mind minute by minute. You really wanna straight things up as early as possible. It will be hard keeping quiet on something that you firmly believe to share with us but its important for you to give proper attention to a child even if its not yours. We are humans, we even get attached to babies of animals, and she is a Human after all. Whatever happens " IT'S NOT THE BABY'S FAULT "
Watching you so loving and caring towards the daughter, i think she will realize her mistake and confess or may be this is your baby. Or else get yourself a DNA tested after 3 to 8 months when you are sure of her being a healthy kid.
A thing that you can do now is to ask the Doctor about the kid, why is she different than you and your wife. May there is a more simpler reason to all your queries, may be there are some medical condition or medications that effected her appearance.
Now, From a FORUM MATE TO A FORUM MATE : Buddy, it's a family turmoil, the best you could have done is talk to your parents or friends. Someone elses family turmoil is someones entertainment, get practical mate.You should not have posted this thread here, what if all your doubts are wrong, she can sue you on Publicly Defaming her. Above all, this is place to find answers to New Business or marketing theory, in such cases talking to offline real Family or Offline Real Friend is helpful.
Live life with a Big Heart