Research on the outcomes of midwifery care is hampered by the lack of appropriate instruments that measure both process and outcomes of care in lower risk women. This article describes an effort to adapt an existing measurement instrument focused on the optimal outcomes of care (The Optimality Index-US) to reflect the contemporary style of U.S.-based nurse-midwifery practice. Evidence for content validity of the instrument was derived from literature reports of randomized clinical trials, synthetic reviews, and the clinical consensus of professional reviewers. Eleven perinatal health professionals and consumers, representing disciplines of obstetrics and gynecology, midwifery, epidemiology, and neonatology reviewed the instrument. The instrument was then applied to an existing data set of women who intended to give birth at home (N = 1,286 women) to determine its utility in measuring events in the process and outcome of perinatal health care as managed by nurse-midwives. Results suggest that the tool holds promise for use in outcomes studies of U.S. perinatal care. Further testing of the instrument among diverse multicultural population groups, with various providers, and in diverse birth settings is warranted.