Uterus Measuring 3 weeks ahead?

Marli • Lottie Mae norm 3-23-20. Liam Thomas🌈 born 4-7-17. Angel baby 5-4-16. Hubby & I married 11-1-14. Have two Pomeranian `babies`.
So today when I went to the midwife she said I'm 27 weeks 5 days, measuring 31 weeks. So about 3 weeks ahead. I've been ahead most of the pregnancy...uterus only supposed to be to belly button at 19 weeks and mine was To my ribs already. 
She didn't seem concerned. She just said it offhandedly and moved on. 
I had an ultrasound two weeks ago and baby looks good / on schedule. Plenty of fluid but not too much. 78th percentile for weight. 
I was diagnosed gestational diabetes. But perinatologist and dietician have both cleared me as my numbers are great. 
So why is my uterus growing ahead of schedule?
Anyone else have this and did it impact your pregnancy?