Two standards have played a dominant role in policies to organize U.S. perinatal care. Minimum volume (or size) and service levels according to technical capacity have been major components of perinatal regionalization and other reorganization efforts. These standards are consistent with structural definitions of quality of care, but not necessarily with quality definitions according to outcome. Empirical research has not demonstrated a general association between the standards and improved perinatal outcomes, although it has demonstrated improved outcomes for very low birthweight babies. The standards have contributed to the growth and financial stability of tertiary-level services, but economy in terms of lower unit costs has also not been demonstrated. These discrepancies between research findings and the paradigm of a system of large, complex centers have led to conceptual errors in explaining findings, but they have also led to a recognition of uncertainty concerning perinatal service organization.