Return to running after pregnancy

So I found out I was pregnant 3 days before I was supposed to run the GM marathon earlier to year. After much deliberation I didn't run the race in the end but did continue running up to 32 weeks then continued with x training then finally swimming at the end. I now have a 4 week old and can't wait to start back running. So what I'm after is any advice from fellow running mums on how you got back into running. How soon did you run, how much did you run, How quick did you get back up to speed. I was a 30 mile a week regular before the pregnancy, doing 50 plus a week when in training for races.