Assuming you are talking about a U.S. citizen based spousal I-130 petition, yes having a child together does help demonstrate that it is a bona fide marriage.
Having a child together is evidence the marriage was entered into in good faith. You can submit a letter from your wife's doctor confirming the pregnancy. The letter can so mention your involvement such as attending appointments if you do.
Certainly evidence of the pregnancy should be included. Are you having the baby in the US? If so you will file more than the I-130 and its related forms.