At the close of this century of immense technological advance there is still debate about how best to determine when confinement is due and whether widely available technology for this should be used for all pregnant women or not. The expected date of delivery (EDD) is a central point in antenatal care. Without accurate knowledge of gestational length the evaluation of fetal wellbeing and fetal growth, as well as the timing of delivery, is bound to be difficult. No one who remembers the uncertainities surrounding gestational age assignment in the time before the advent of modern ultrasound wishes a return to those times, anymore than it is unthinkable that the telephone, televison, microwave owens, fridges, calculators or computers can be dispensed with from our lives. No one would start a flight today without using the necessary electronic devices to enable safe flying, although this may have been done fifty years ago. It may then seem strange that ultrasonic measurements of the fetus, which enable gestational length to be assessed with good accuracy, should not be universally accepted. The last menstrual period (LMP) is still widely preferred for assigning gestational age, even where there is free access to modern ultrasound.