Larger than expected.

So I went into my OB Appointment today and I’m supposed to be 20+2. Well the nurse practitioner wanted to measure my stomach because she noticed I was showing more than she expected for someone who is 20w with their first. She measured my bump and said it was measuring as if I’m 26 weeks instead of 20. But I still 10 lbs less than my pre-pregnancy weight. They are going to schedule me for a “high risk growth ultrasound” at the hospital, just to make sure baby girl is ok, but I’m kind of nervous. I have had a hunch since the beginning of the pregnancy that I’m having twins. My husband is a 3rd generation twin and twins slightly run on my side. Could this be the reason I’m measuring large? My last ultrasound was at 10 weeks.

Any ideas what it could be?