Baby weight

my OB has always been mentioning that my baby is a little bit bigger since week 20. ive read in other apps that they usually judge a baby's weight through their femur length? during my last appointment in week 32, he asked me to watch my diet and eat healthier. I think the only thing u need to worry about is if the baby is too big, u might need c section instead. otherwise, u should know that it's just an estimation of ur baby's size, the actual might differ.