A series of uncomplicated pregnancies presenting during the first trimester for elective termination was assigned a gestational age using accepted ultrasonographic nomograms. Following termination by suction curettage, the proportion of nucleated erythrocytes (NRBC) and anucleated erythrocytes (RBC) present in the placental circulation was estimated from hematoxylin and eosin-stained slides of the chorion frondosum using a 10 point scale. The score correlated tightly with sonographically assigned gestational age assessment between 15 and 45 cm crown-rump length (CRL) (48 and 83 days of gestation). These findings suggest the following: (1) the maturation of RBCs follows a course that is tightly correlated with gestational age; (2) an assessment of RBC morphology and, thus, an estimate of gestational age can be provided using routine histopathologic techniques and study of the placenta only; (3) this method may prove to be particularly useful in cases of unexplained spontaneous losses as a means of investigation when cessation of fetal development occurred.