High Risk?

So I'm 17 weeks, and so far my doctor has said everything is healthy, and didn't mention anything about any issues at my appointment a week ago. However I just got a call from a high risk doctor saying that I was referred to them and asking me to schedule an appointment?? What could that mean? Why wasn't I told I was being referred??

*edit* I'm 21 and at a healthy weight range, no prior history of any health issues other than Scoliosis when I was younger, but the curvature was very slight and my doctor said it was no issue. So far all my vitals have been perfect