Age determination of early human embryos and fetuses.

Since the number of legal abortions has increased, it has become possible to get human embryonic and fetal material for developmental and teratological studies. Unfortunately this material, due to gynaecological techniques, is usually not intact and thus the estimation of fetal age from crown-rump length is impossible. Usually, however, one or both feet are available; thus, in this paper, foot lengths of 201 embryos and fetuses are correlated with menstrual ages. The mean foot lengths are from 2.9 to 18.5 mm and the age range from 7 to 16 weeks, respectively. Comparison with Streeter's measurements (1920) is also made.