Yah sorry dont have a clue...never knew babies can have them while in tummy either. But then like Emz said it could be Hormonal...I had a cyst on my overy when I got pregnant with this one and it is gone now, it could be the same with baby...here is hoping all is well at your next scan.
Try not to worry your slef until you know for sure what it is. I know its hard but Just be positive!!
Big Hugs