Uterus measuring large, but baby right on track?

Stacy • Expecting our 5th baby 12-1-15. Proud mom of an 18, 15 and 4 yr old...missing our angel baby 11-27-14.
So I am exactly 10 weeks today and baby is measuring 10 weeks 2 days. My Uterus is measuring 16cm. Has anyone ever measured this large so early? Only one baby on the ultrasound. I am thinking it's due in part to the stillbirth I had at 35 weeks on Thanksgiving, but the ultrasound tech still seemed puzzled by it. Any other theories?