Perigestational Collection?

Heather
I went in for an ultrasound at 6 weeks exact on October 19th. I got an ultrasound to date my pregnancy and get a due date. When they did the ultrasound they never told me anything was wrong she acted normal. When I got back in my room the doctor came back in and told me that they saw a perigestational collection and wanted me to come back in in 2 weeks, which will be November 1st. They want to do another ultrasound to see what thecollection does. I'm just wondering if anyone else has had this and what happened? I'm nervous bc he gave me a shot of rhogam "just to be safe" and I normally don't get that until 28 weeks. This is my 3rd child. This is the ultrasound he gave me for my baby but he didn't give me one showing the collection and I have no idea if they clear up or get worse and what happens.