Work hours, shift length, and off-hours shifts have been implicated as contributors in medical errors and poor outcomes, suggesting that interventions addressing circadian physiology and fatigue in health care workers may improve clinical outcomes. Several European and Canadian studies report associations between time of birth and maternity complications, but US studies on the influence of time of day and weekend births on maternal and neonatal outcomes are limited and present mixed results. Pregnancy-related morbidity and mortality are rising nationally, and the accuracy of previous maternal morbidity estimates has recently been questioned. The relationship between time of day and maternity outcomes is a potentially important patient safety issue that remains poorly understood. This study will evaluate the current scope and severity of maternal and neonatal morbidity and mortality in California, and test for relationships with time of birth.