33+4 weeks with di/di girls

Bree • Baby girl born 6/30/15 Twin girls born 3/3/18

I had an ultrasound today to check on size and one is weighing at 4.8 and the other is 5.2. That seems big to me for twins at this point. Doctor said he won’t let me go past 39 weeks so with average weight gain of .5 a week that’ll put these girls around 7.3, 7.8 pounds at birth. I thought twins were usually smaller then singleton babies at birth??