I had a large Corpus luteum cyst at my 7 week scan. It was almost 10cms but my GP didn't even bat an eye lid, she advised that they were quite normal. I did some research though and read that a lot of women get the cysts monthly but it passes along with the unfertilised egg (or something similar). Mine had disappeared by my 20 weeks scan but I was very nervous waiting to check that it had gone. I hope everything else works out ok and you can get lots of hugs off your big babies!