Objective: This study was undertaken to determine the occurrence rates, outcomes, risk factors, and timing of obstetric delivery for trauma sustained during pregnancy. Study design: This is a retrospective cohort study of women for trauma in California (1991-1999). International Classification of Disease, ninth revision, Clinical Modification codes, and external causation codes for injury were identified. Maternal and fetal/neonatal outcomes were analyzed for women delivering at the trauma hospitalization (group 1), and women sustaining trauma prenatally (group 2), compared with nontrauma controls. Injury severity scores and injury types were used to stratify risk in relation to outcome. Statistical comparisons are expressed as odds ratios (ORs) with 95% CIs. Results: A total of 10,316 deliveries fulfilling study criteria were identified in 4,833,286 total deliveries. Fractures, dislocations, sprains, and strains were the most common type of injury. Group 1 was associated with the worst outcomes: maternal death OR 69 (95% CI 42-115), fetal death OR 4.7 (95% CI 3.4-6.4), uterine rupture OR 43 (95% CI 19-97), and placental abruption OR 9.2 (95% CI 7.8-11). Group 2 also resulted in increased risks at delivery: placental abruption OR 1.6 (95% CI 1.3-1.9), preterm labor OR 2.7 (95% CI 2.5-2.9), maternal death OR 4.4 (95% CI 1.4-14). As injury severity scores increased, outcomes worsened, yet were statistically nonpredictive. The type of injury most commonly leading to maternal death was internal injury. The risk of fetal, neonatal, and infant death was strongly influenced by gestational age at the time of delivery. Conclusion: Women delivering at the trauma hospitalization (group 1) had the worst outcomes, regardless of the severity of the injury. Group 2 women (prenatal injury) had an increased risk of adverse outcomes at delivery, and therefore should be monitored closely during the subsequent course of the pregnancy. This study highlights the need to optimize education in trauma prevention during pregnancy. (C) 2004 Elsevier Inc. All rights reserved.