Hi, I have a question regarding my baby size (I am 31w5d pregnant) I had an ultrasound today, my baby s FL measures over 34w, and its HC measures 31w6d. The FL is over 90 percentile, which makes sense, but the HC is only 18 percentile. Since the HC measure is very close to its gestational age, I thought the percentile should be close to 50, but why is it 18 percentile?