How long after a miscarriage was approximately 4 weeks pregnant do i have to wait before trying to conceive again?

Ok to try right away: Older recommendations were to wait for 2 normal menstrual periods to pass; but newer research does not show an increased risk for miscarriage if women conceive immediately after a miscarriage. So as soon as a woman feels emotionally ready to try again, it should be safe, barring any complications.

Waiting: I assume you mean an uncomplicated miscarriage. Reasons include 1) your HCG level from the miscarriage must fall to zero, 2) you must resume ovulating, and 3) you must re-establish a cyclic endometrium. I recommend waiting 1 full cycle after an uncomplicated miscarriage and confirming the HCG has fallen. Many doctors recommend a longer wait, but it seems arbitrary to me after 1 cycle.