The accuracy of ultrasonic measurement of fetal crown-rump length

Abstract Routine ultrasonic crown-rump length measurements were retrospectively evaluated in an antenatal clinic using maternal body temperature graphs as reference to ovulatory age. A comparison with the original figures of Robinson is made. Potential errors are discussed. The conlusion is that one should be very careful in interpreting an ultrasonic CRL measurement before 10 weeks menstrual age because of both measurement and operator errors.