The assessment of prenatal age from the crown‐rump length determined ultrasonically

Abstract

Crown-rump lengths determined ultrasonically in vivo and in utero in cases of known postovulatory age (33-86 days) agree well with those in length/age tables in current embryological usage. Within the embryonic period proper, however, for a given age, the ultrasonic lengths are usually 1 to 5 mm longer than those of fixed specimens. The probable reasons for this are discussed.