Biochemical tests of fetal well-being ('placental function tests') have been part of routine obstetric practice for more than twenty years. This book provides an overview of the current status of these tests - the physiological basis for their use, and their advantages and limitations in clinical practice. Considerable attention is given to interpretation, a subject which in the past has led to much confusion both in the scientific literature and in the minds of clinicians. Recent advances are described in detail, in particular the discovery of a whole new generation of placental products some of which offer great promise in the prediction of conditions, such as placental abruption and premature labour, which cannot be identified by any other current parameters. Finally, a set of clear recommendations is put forward for the choice of test in most of the common complications of both early and late pregnancy. The emphasis throughout is on how the basic biology of fetoplacental products dictates their use and interpretation in pathological conditions.