What is the fine-grained topic of the following text: Historians have analyzed and interpreted birth statistics, medical textbooks, medical school curricula, minutes of medical society meetings, public health reports, articles in medical journals and popular magazines, letters from laboring mothers, diaries of midwives, legislative committee reports, and state legislation to identify issues of class, race, gender, and professional and economic competition that may have played a role in physicians' opposition to midwives and the transition from lay midwife-assisted home births to physician-assisted hospital births in the United States. Only return the topic.
Physicians' opposition to midwives and the transition from midwife-assisted home births to physician-assisted hospital births in the United States.