Constructing standards. Ultrasound is today the authoritative method for estimating gestational age and diagnosing abnormal development. But for it to achieve this status standard parameters and normal ranges first had to be determined. Donald’s team measured the distance between the left and right sides of the fetal head. This (‘biparietal’) parameter had already been used to estimate head size and predict pelvic disproportion, and was now recast as an indicator of fetal growth and development. Crown–rump length, first introduced by Franklin P. Mall in the early twentieth century, regained popularity as a means of dating early pregnancy. Sonography was compared with standards developed in other fields, such as Carnegie stages but mostly relied on the date of the last menstrual period in patients with regular cycles. With its wider adoption, large populations have been scanned to construct national and international standards, but it is still contested whether ethnic groups should have their own charts or differences should be explained by socio-economic factors.

Uses of ultrasound

Ultrasound was quickly accepted as a diagnostic tool, but the modes of use, frequency of examination and norms of safety and fetal development are still not fully standardized.

Between the 1950s and 1970s, physicians, physicists and engineers debated whether the scan should show a morphological image, akin to X-rays, or a graphical representation of deviations from the norm, like an electrocardiograph. In obstetrics the morphological orientation won, but different countries decided differently about frequency of use and indications for scanning, depending on whether ultrasound was framed as a diagnostic aid solely for pregnancies at risk, or a routine screening device for all.

Uses expanded beyond diagnosis. Around 1970, psychologists proposed that ultrasound could help the concerned mother ‘bond’ with the future child. Yet that bonding would have to be mediated, because at the time no untrained eye could interpret the scans. Professionals did this instead: obstetricians, midwives and specialized sonographers. Gradually, easier-to-read sonograms came to occupy a symbolic place in late twentieth-century popular culture. Many parents’ first visual encounter with their child was no longer at birth but seeing the gestational sac—a bright ring around a clear centre, characteristic of early pregnancy—or, even more powerfully, the embryonic heart beating on an ultrasound screen.

‘Control of life’ in Life, 1965


Interpreting ultrasound scans, 1963