My first reaction is that four months is a long jump for a scene break and would be better as a chapter break. However, there's a lot of "it depends" attached to that thought. One is that if you have many long jumps in time, then the weight of this one becomes less, so it could go either way.
Another relates to the length of all your chapters and how far into the current chapter this occurs. If you're trucking along with a consistent chapter length, suddenly having a very short chapter would be conspicuous, so a scene break might be better.
Yet one more depends on how closely the scenes immediately before and after the break are related. If it's a direct follow-on, except for the elapsed time, then that favors a scene break over a chapter break. But if the scene following the break deals with a different plot thread, it doesn't really affect the decision one way or the other.
Chapter and scenes breaks probably shouldn't be used as a "passage of time" tool. This is a natural stopping point for the reader, and you don't want to give them a easy out to put your book down. If you can end every scene and chapter with a "question" (cliffhanger, foreshadowing, questions, mystery, shocking revelation, etc) they want to know the answer to, you keep them reading and wind up with a book they just can't put down. (Which usually means a winner on the publishing front)
Actually, a scene or chapter break is exactly the right place to make a jump in time or space. Yes, you need an unresolved question to carry the momentum over the break, but there's nothing wrong with an unresolved question hanging in limbo for some time before being answered. If nothing important happens during those four months, don't write four months worth of nothing.
If you're ending your chapter on the revelation that the baby isn't his, that's a pretty good spot. If this is new info to the reader as well as the hubby, they'll turn the page to see how the wife and hubby react to this news. I personally, get very annoyed with authors who drop a great plot bombshell in my lap then skip ahead and don’t let me see how it plays out. The conflict is where the fun is. So I’d be wary of skipping the resolution or reaction to this conflict and moving ahead four months.
I agree you shouldn't use a jump to dodge writing an important scene, but the OP didn't give enough information to assume this. It's equally possible the immediate aftermath has already played out, and the chars are in a stalemate until something triggers a new move.
