Baby bigger than glow says

Sonel • I have a beautiful little boy of 10months and looking to get back to tracking my cycles for bubba nr 2!
Hi ladies! Just had my 16 week scan and it shows baby is 189g (6 1/2 oz), but glow says baby should be 100g (3 1/2 oz) this week. How can it be so far wrong? My boy is  almost double what glow says. Anyone else experienced this? Why is my baby so big? Should I be worried about gestational diabetes?