Sunbeam-your body naturally releases the LH surge just before ovulation so when you are on an ivf cycle the orgalutran supresses that LH surge so when you have the trigger injection it gives you that surge so the eggs go through the last stage of maturing ready for collection and it also means it is timed right so they don't ovulate to early and are missed be the doctor because it take roughly 36-38 hrs after that surge for the eggs to be ovulated.
Try not to worry about your scan you have some m/s so that is a good sign you will do fine.