I have three kids (5, 5, 2) and can't kick the desire for one more. My husband is fine with stopping and fine with having another. He is 40. I would be 38 at delivery if I got pregnant within the next 6 months.
We aren't super wealthy by DC standards but finances don't really factor into this decision (our home is large enough for 4 kids, we already have a van, our vacations (beach house several weeks a year) wouldn't change, we live in an area with goods schools (that my older two already attend), etc. We already said goodbye to elaborate vacations, luxury goods, private school, etc when we had child #3. #4 wouldn't change much.
The one thing I worry about is age. 38 is NOT too old to have children by any means but it gives me pause when I already have 3 kids. Would you have child #4 at age 38?