The process of technological change in obstetrics must be understood as contingent on the exigencies of the professional project, rather than in terms simply of improvement or dehumanization of care. Transformation in the procedures by which the female pelvis and the fetal head have been measured illustrate this point. The development of new measurement techniques was profoundly influenced by the shifting locus of obstetric care and by changing professional concerns, including the initial demarcation of a professional practice and subsequent debates (...) about preferred modes of intervention. (shrink)