I also experienced a chemical pregnancy once (among many other failed cycles) and it took about a week for AF to arrive. I think, yes, the hcg needs to be close to zero for AF to arrive, I never had my hcg tested after the 4th one... I just watched my hcg decrease with each test (40, 80, 32, 16). And yes, I can remember just wanting to get it all over with so I could try again. With the chemical pg, I made another attempt right away... the chemical pregnancy was almost like having a late, somewhat heavy AF and so I started again the next month. Some RE's want you to have one normal AF in between, but it's not really necessary. So sorry Mrs. M for your chemical, it's such a cruel result.