A retrospective analysis of the ultrasonic growth patterns of 16 cases of trisomy 18 is presented. The
patterns were examined by the crown-rump length in the first trimester and by the biparietal diameter and
femur length in the second trimester or later. The crow-rump length of trisomy 18 fetuses was smaller
than normal. Significant growth delay detected during the first trimester may be a useful marker for
trisomy 18. The biparietal and femur growth expressed the low profile type in trisomy 18. The growth of
biparietal diameter and femur length was below the 5th percentile from early in the second trimester, but
usually without cessation. The femur length was more retarded than the biparietal diameter. The
biparietal diameter/femur length ratio may prove superior to trisomy 18 screening methods.