Thickening on fetus?

Morning mamas! We had our ultrasound yesterday at 10 weeks 4 days and the doctor noted “thickening on the back of the fetus” and has referred us to a specialist to have another ultrasound done. Has anyone else had this noted and what was your outcome? They said it could be nothing and I’m not worrying myself out about it since we can’t change anything. But id love to hear from anyone else who had this