In an open-access article from the Journal of the American Medical Association (JAMA), researchers report that, among more than 34 million hospital births in the U.S., 37.4 percent of the hospitals were low volume. Among low-volume hospitals, 18.9 percent were isolated and 58.4 percent of these were rural.
See JAMA: Birth Volume and Geographic Distribution of U.S. Obstetric Hospitals, 2010 – 2018 for the article.