baby,
actually most of us dun get the 4wk scan cos is really too early to see anything. most of the time 6 wk scan is the first scan. maybe cos u had bleeding so dr being more cautious.
after 6 wk scan, next scan is abt 3 wks later at 9 wks then 12 wks. once u cross 12 wks, dr visit will be every 4 wks. when u hit 30wks, visit go back down to every 2 wks then every wk after 35/36 wks.