Baby’s arm swollen on ultrasound

Posting in multiple groups for feedback. Having my 4th child. I’m 21 weeks today, earlier this week I had an ultrasound and the lady was concerned with baby’s arm. She said it was swollen from what we could see and that she wanted the doctor to come in to look at it and maybe he could tell us what was going on because she’s never seen this. He came in and said things like this happen but it can be many reasons, I was there for hours before he came in. He told me I would have to go to hospital for a more detailed scan and they would be able to figure out what’s going on. I included a pic on here. If anybody has seen this or experienced this with any of their children in the womb please let me know. The hospital has been so busy , I’ve been unable to get through the scheduling line but I’ve been worried ever since. His right arm is what’s shown by his head, his left arm is the swollen one in the other ultrasound