Twins weight

Dee
At 31 weeks I went to my high risk for and Twin A weighed 3.12 and Twin B weight 4.2. Today I had another US and Twin A is 4.3 and Twin B is 5 lbs even! They're fraternal ton boys. 
The tech checked the cords and didn't seem concerned. I think almost a pubs difference is huge. Anyone else have this happen? If so, what was the outcome?