Views and attitudes. towards termination of pregnancy have shown con siderable evolution over the past few decades. Along with these changes has come a growing concern to adopt means and methods which could make termination easier, safer and more effective. In this evolution, termination in the second trimester in par icular is notable as being responsible for a dis proportionate share ofthe complications and adverse experiences associated with pregnancy termination. Although the almost universal shift towards earlier abortion has reduced the number of second trimester procedures as a percentage of the whole, the problems of interrupting pregnancy in the second trimester remain conspicuous. Delay in either seeking or obtaining abortion is still, in many parts of the world, all too frequent. AdditiDnally, recent developments in the prenatal diagnosis of fetal malformations, alphafeto protein screening programmes and changes in the pattern of and approaches to intrauterine fetal death now also place greater emphasis on the need for adequate methods of interrupting pregnancy in the second trimester. Unlike the first trimester in which vacuum aspiration is universally con sidered to be the method of choice, in the second trimester of pregnancy the clinician is faced with alternatives; one method may be more appropriate than another in a particular circumstance and no single method is unequivocall accepted as best. Neither do second trimester terminations form a neatly defined single category."

In recent years there has been an impressive surge of interest in the mecha nisms which control the onset and the maintenance of labour. Much of it stems from a constant awareness that gestational age at birth is still an important factor in neonatal mortality and morbidity. Advances in the sensitivity and specificity of immunoassay, the discovery of the prosta glandins, new skills in fetal surgery and chronic catheterisation in experi mental animals have greatly stimulated further research in this area. In the meantime clinicians became continuously more aware that, despite consider able advances in perinatal medicine, gestational age at birth remains the major determinant of neonatal mortality and morbidity. It led them to seek new and better ways of controlling uterine function whether by influencing cervical ripeness, by stimulating or by inhibiting myometrial contractility. This volume uniquely combines knowledge which has been gained from both experimental and clinical research on parturition. A brief outline of current evidence on the control of parturition in experimental animals may be fruitful in delineating problems and hypotheses for further study in human pregnancy. Much of our present day knowledge of human parturition has been gained by checking such data against experimental findings, careful measurements and clinical observations in human pregnancy. It is hoped that the interdisciplinary nature of this volume will enhance the understanding of human parturition and stimulate further research in this area. Thanks are due to Miss H. Wittenberg and Mrs M."