Placental localization with the A-scope was in practice for a some time in the late 1950s and early 60s, although results were far from satisfactory. The placenta is located by noting the presence of characteristic A-mode echo patterns (secondary to increase in vasculature) of the placenta between the uterine wall and the fetus. The tip of the placental edge however remained difficult to define.
B-mode placentography has not been taken up until 1965 by the Denver group (Thompson and Gottesfeld) using bistable equipment. The definition of the placenta was still unsatisfactory, particularly those which are posterior lying. The situation was improved with the arrival of the "grey-scale".
Image courtesy of KretzTechnik®, Zipf, Austria.