Although delivering babies was woman's work from earliest times, it has become an occupation dominated by a male-oriented medical profession in modern times. In the United States it has been monopolized by male obstetricians. As the change occurred historically, childbirth was redefined as a medical rather than a social event, and the roles and care surrounding it were reorganized to suit medical needs. The following cultural factors contributed to these changes: industrialization, urbanization, the building of hospitals, the development of scientific knowledge and medical technology, ratios of physicians to population, and the political power of medical associations.