When is enough enough?

Amy • 33 with 2 beautiful children! Happily married for 11 years!
Just had my 4th mc. I have 2 wonderful children but we really want another. Just not sure when we should stop trying. Last years I was 20 weeks along. That was by far the most devastating but they all have been. Will I just know when I should stop? :-( its so hard. I don't wanna go through the loss again.