I had my anatomy scan at 20 weeks of pregnancy. cerebellum only measured 18 wks. doc said she didn't have time to go over scan that day. i'm worried! ?

Consider level II: It may be that your dates are not correct. Or there may be an issue needing follow up. Try to find out if you are in need of a "level II" or detailed ultrasound from a maternal fetal specialist, or high risk pregnancy doctor. This is not saying your pregnancy is high risk, just that the ultrasound may warrant a second look.