This book is the product of the efforts of a number of people dating back to 1956, when Professor T. Kemp, then head of the University Institute for Human Genetics in Copenhagen, proposed a study on the importance of x-ray irradiation in pregnant women. Under the guidance of Professors Dyhre Trolle and Preben Plum of the Uni versity Hospital in Copenhagen, the investigation was expanded to deal with prenatal and perinatal factors of importance for the development of the infant. The corpus of medical data that resulted from these efforts was collected and organized by Drs. Bengt...