1st early scan ultrasound! Twins???

I went in today for my first visit. Measured 5 weeks 5 days. I had a miscarriage in November so my doctor wanted to see me right away and had me do bloodwork before my visit. So.... I had a blood test Friday afternoon and my Hgc numbers were a little over 6,000. I went Monday and they more than tripled at 19,450. The first thing he said was healthy numbers and possibility of twins?! On the ultrasound we just saw one sac but he wants me back in 10 days. Has anyone experienced this? What’s your take on the hgc levels- are they high?!