I had a cyst on one of my ovaries as well which was picked up at my dating scan. It was about 7.5cm.
We required a few extra scans just to keep an eye on it but in the end, by our 19 week scan it was gone!
We were told that basically there is nothing they can do but it will be monitored for growth. They don't affect bubby at all but it can be very painful if they burst. And they burst spontaneously as your belly gets bigger.
Apparently it's really common in pregnancy because of the extra hormones and more often than not they will just disappear.
I don't think it's anything to worry about but your doctor can give you all the info when you see them.
I actually posted a similar thread when I found out I had one and I got heaps of replies from the ladies saying they had also had them so it does appear to be really common
Good luck and I hope that helps
Mama to 3 gorgeous boys
Cole ~ 18 May, 2007
Cooper ~ 17 August, 2009
Hudson ~ 25 February, 2011