Birth defects have assumed an importance even greater now than in the past because infant mortality rates attributed to congenital anomalies have declined far less than those for other causes of death, such as infectious and nutritional diseases. As many as 50 % of all pregnancies terminate as miscarriages, and in the majority of cases this is the result of faulty intrauterine development. Major congenital malformations are present in at least 2 % of all liveborn infants, and 22 % of all stillbirths and infant deaths are associated with severe congenital anomalies. Not surprisingly, there has been a great proliferation of research into the problems of developmental abnormalities over the past few decades. This series, Advances in the Study of Birth Defects, was conceived in order to provide a comprehensive focal source of up-to-date information for physi­ cians concerned with the health of the unborn child and for research workers in the fields of fetal medicine and birth defects. The first four volumes featured recent experimental work on selected areas of high priority and intensive investigation, including mechanisms of teratogenesis, teratological evaluation, molecular and cellular aspects of abnormal development, and neural and behavioural teratology. It seems logical and timely that the clinical aspects should now be presented. Accordingly, leading experts were invited to review a broad range of common problems from the standpoint of embryology, aetiology, clinical manifestations, diagnosis and management. This volume deals with genetic disorders and prenatal diagnosis.