Fetal monitoring. Biochemical methods

Biochemical tests of fetal well-being are falling into disfavour. Difficulties arise because we are unable to ascribe specific functions to most test substances, and because they have a large normal range. Nevertheless, a critical survey of the evidence suggests biochemical tests have a part to play in antenatal monitoring, albeit a much reduced one. The main test substances are steroids and proteins produced by the trophoblast. These two classes of substances have a quite different metabolism and compartmental distribution, and the appropriate application of assays is different. A variety of progestogens and oestrogens are used as test substances, the most notable being oestriol. In view of their rapid metabolism, steroid assays serve best in pathological conditions of rapid onset. A dynamic test of the conversion of dehydroepiandrosterone to oestradiol has not fulfilled its initial promise. Among the placental proteins, human placental lactogen is most favoured, although some of the newly discovered proteins may have special applications in certain diseases. The use of biochemical tests in early pregnancy has not been sufficiently explored. The test substances may, in early pregnancy, play a more important role in fetal development and biochemical tests, particularly as a screening test to detect patients at risk of later overt disease, may be valuable.