16weeks 6days baby weight

Natasha
I had an U/S with my high risk MD today to see my twin girls (every two weeks). The U/S measured them 16weeks 6days with 6ounces each.
The app and many other sites said that the baby weights an average of 3-3 1/2 ounces at this stage!. 
I asked my doctor about the target weight and he said they are both within the expected size and weight for the stage.
I keep thinking that it's a little bit more than average if they weight double the standards on the app and other baby sites.
MD assured me that the sizes are fine and they are healthy.
Do you guys have a similar issue with the weights?Thanks