Background Incidental pregnancy in trauma patients is associated with a high fetal mortality. Because of quality assurance reasons, many trauma centers have eliminated the rapid urine pregnancy screen. We sought to determine the utility and impact of the initial ultrasound examination in the diagnosis of pregnancy in female trauma patients. Methods Data were analyzed for all female trauma patients in whom pregnancy was diagnosed during a 5-year period. Results One hundred one (70%) of 144 pregnant women had an initial ultrasound examination. Eighteen patents had newly diagnosed pregnancies, of whom 8 of 9 patients (89%) at ≥ 8 weeks’ gestation were diagnosed by the initial ultrasound. This directly contributed to a significant decrease in the amount of radiation exposure (p < 0.001) compared with patients diagnosed by serum β-human chorionic gonadotropin. Conclusion An initial ultrasound examination should be considered in all female trauma patients of reproductive age. This may help to promote a reduction in fetal radiation exposure.