Maternal blood flow to the placenta

In the late 1940s, Beker (J Obstet Gynae Br Emp 1948;55:786–65) and Bastiaanse and Mastboom (Ned Tijdschr Geneesk 1949;93:2609–18) hypothesised that placental hypoxia could be the trigger for pre-eclampsia. However, no reliable technique existed at that time to assess maternal blood flow to the placenta. In 1953, McClure Brown and Veall from the Hammersmith Hospital in London described a technique to measure maternal blood flow to the placenta in normotensive and hypertensive pregnancies (J Obstet Gynae Br Emp 1953;60:141–7). They blindly inserted an 18-G needle infusing procaine for analgesia, until they could tap blood from the choriodecidual space. At that point, saline marked with radioactive sodium was rapidly injected with a specially designed tool (Figure 1), and the radioactive decay curve over the placenta was drawn with a Geiger counter. The radioactive sodium washout was thought to be correlated with maternal blood flow, and was slower in hypertensive women, suggesting a 60% reduction in blood flow compared with controls. The Doppler principle was first described by Christian Andreas Doppler in Austria in 1842. Medical applications of ultrasonic Doppler techniques were first implemented by Shigeo Satomura and Yasuhara Nimura at the Institute of Scientific and Industrial Research in Osaka, Japan, in 1955 for the study of cardiac valvular motion and pulsations of peripheral blood vessels (Kaneko Ultrasound Med Biol 1986;12:187–95). The Satomura team, which also included Ziro Kaneko, pioneered transcutaneous Doppler flow measurements in 1959, several years ahead of similar work at the University of Washington in Seattle, USA. It has also become known from the work of Ziro Zaneko and Kanemasa Kato in Satomura's laboratory in 1962, that blood flow can be detected by the ultrasonic Doppler method, largely because blood itself consists of a suspension of ‘uncorrelated point back-scatterers’ (the red cells) with varying density and compressibility, and not because of turbulence in the flow stream as previously thought. In 1966, Kato and Izumi pioneered the directional flow-meter using the local oscillation method where flow directions were detected and displayed. This was a breakthrough in Doppler instrumentation as reverse flow in blood vessels could then be documented. Stuart Campbell and David Griffin at King's College Hospital in London suggested, in 1983, that the shape of the arterial flow velocity waveforms would be more useful in fetal assessment. In the same year, Campbell et al. also reported on the association of abnormal uterine and placental arcuate arterial waveforms with proteinuric hypertension and low birthweight (Lancet 1983;1:675–7). A few years later, Trudinger et al. confirmed that uteroplacental blood flow is reduced in pregnancies complicated by fetal growth restriction or pre-eclampsia (Br J Obstet Gynaecol 1985;92:39–45). This paved the way for non-invasive assessment of uteroplacental blood flow, and for studies on the early prediction of pre-eclampsia, such as the one published by Sovio and Smith in this issue of BJOG (BJOG 2019;126:963–70). The authors declare no conflicts of interest. Completed disclosure of interests form available to view online as supporting information. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

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