My OB recommended every 2nd day from day 12. But we used OPK's and did it morning & night the day I got the positive. (Plus DH was about to go overseas so kinda wanted a good supply swimming around in there! LOL). This is probably TMI but we also did it so that DH 'went' first, and then he made me 'go'. Apparently this dips the cervix into all the spermies and sucks em up closer to the egg. hehe. Well... something worked!! I guess we'll never know if it was coz of that, or just good timing