Recent Advances in Foetal

In I90I Ballantyne's ' Plea for a promaternity hospital' led to the first establishment of hospital beds for the specific purpose of studying the physiology and pathology of pregnancy. Although he quickly realized and strongly urged. the value of antenatal care to the mother, Ballantyne's original aim was chiefly to discover means of saving foetal life ' to prevent miscarriage and that most terrible of all events the dead birth, and to cure before birth the diseases and deformities of the foetus.' Parsons (1946) has emphasized that infant care must begin before birth, and only by a study of the normal can we hope to understand the abnormal. For this reason a mere obstetrician ventures to review a little of the recent work of physiologists, arbitrarilv selecting topics suitable for inclusion in a short article. Oxygenation of the foetus. Barcroft and many others have made great contributions to this subject. The foetal tissues require large amounts of oxygen, 1.25 ml. per kilo per minute at term (Haselhorst and Stromberger I932), and special physiological mechanisms are necessary to supply the increasing foetal demands, though it cannot be overstressed that there are wide differences between the placentae of different species, and the results of animal experiments must not be applied to man without reserve. i. Increased oxygen could be supplied by increasing the oxygen content of maternal blood, but actually the oxygen capacity of maternal blood falls during pregnancy to 15.5 volumes per cent. (nornmal I9 vols. per cent.) because of the lowered red cell count and reduced alkali reserve. 2. An increased flow of maternal blood through the uterus would serve the same purpose, and in fact occurs, but in rabbit experiments the flow lags behind the increasing foetal needs, as is shown by the progressive fall in the oxygen content of the blood in the uterine veins. (Barcroft et al., 1933, 1934.) 3. An increased flow of foetal blood through the placenta would have the same effect. The foetal blood pressure rises progressively during pregnancy in the sheep and the volume of blood traversing the placenta increases, though at term the gain is only proportional to the rise in foetal weight. (Barcroft et al., 1939.) 4. The ' diffusion constant ' of the placenta might alter, that is the ease with which oxygen can cross the placental barrier. Diffusion is slow in the syndesmochorial placenta of the cow., but this observation cannot reasonably be applied to the human haemochorial placenta: In late pregnancy the trophoblast covering the villi is thinner, but the total area of villi does not increase after mid-pregnancy after which maximal foetal growth occurs. 5. The foetal blood has an increased avidity for oxygen. Foetal blood at term contains over 15.5 gm. of haemoglobin per ioo ml. and has an oxygen capacity of 2I volumes per cent. It is commonly stated that this is due to a high red cell count, but during early foetal life the count is low, and at term human cord blood is not polycythaemic. The polycythaemia appears within an hour after birth (Wintrobe and Schumacker, 1936). But though the corpuscles are not more numerous, they are larger and have a higher mean haemoglobin content. The interesting discovery has been made that in many species foetal haemoglobin has different qualities from adult haemoglobin. In the goat, for example, Barcroft and his coworkers (1934) found that the oxygen dis474