Would 14 weeks be too early for the routine anatomy ultrasound compared to doing it at 18-20wks? would there be a big diff in fetal size 14wk vs. 18wk?

Talk to MD: The perinatologist is the best one to answer this question. Yes there is a big difference in size between a 14 wks fetus to a 20 week fetus, so yes it will be easier to do a screening ultrasound with a bigger baby. However, if you have concerns related to your pregnancy, or perhaps difficulty with a previous pregnancy, you should talk to md.