This study assessed labor and delivery (L&D) unit space and design, and also considered correlations between physical space measurements and clinical outcomes. Design and human factors research has increased standardization in high-hazard industries, but is not fully utilized in medicine. Emergency department and intensive care unit space has been studied, but optimal L&D unit design is undefined. In this prospective, observational study, a multidisciplinary team assessed physical characteristics of ten L&D units. Design measurements were analyzed with California Maternal Quality Care Collaborative (CMQCC) data from 34,161 deliveries at these hospitals. The hospitals ranged in delivery volumes (<1000->5000 annual deliveries) and cesarean section rates (19.6%-39.7%). Within and among units there was significant heterogeneity in labor room (LR) and operating room (OR) size, count, and number of configurations. There was significant homogeneity of room equipment. Delivery volumes correlated with unit size, room counts, and cesarean delivery rates. Relative risk of cesarean section was modestly increased when certain variables were above average (delivery volume, unit size, LR count, OR count, OR configuration count, LR to OR distance, unit utilization) or below average (LR size, OR size, LR configuration count). Existing variation suggests a gold standard design has yet to be adopted for L&D. A design-centered approach identified opportunities for standardization: 1) L&D unit size and 2) room counts based on current or projected delivery volume, and 3) LR and OR size and equipment. When combined with further human factors research, these guidelines could help design the L&D unit of the future.