INTRODUCTION: Weight gain in pregnancy is expected; however, excessive gestational weight gain and postpartum weight retention (PPWR) can cause long-term changes to a patient's body mass index (BMI) and increase the risk for adverse health outcomes. This phenomenon is understudied in active duty military women, for whom excess weight gain poses challenges to readiness and fitness to serve. This study examines over 30,000 active duty military women with and without preeclampsia to assess changes in BMI postpartum. MATERIALS AND METHODS: This is a retrospective analysis of claims data for active duty military women, aged 18-40 years, and experiencing pregnancy during fiscal years 2010-2014. Women with eating disorders, high-risk pregnancy conditions other than preeclampsia, scheduled high-risk medical interventions, or a second pregnancy within 18 months were excluded from the analysis. Height and weight were obtained from medical records and used to calculate BMI. Women with and without preeclampsia were categorized into BMI categories according to the Centers for Disease Control and Prevention classification of underweight (BMI < 18.5), normal weight (BMI 18.5-24.9), overweight (BMI 25.0-29.9), or obese (>30.0). Linear regressions adjusted by age and race were performed to assess differences in prepregnancy weight and weight gain, retention, and change at 6 months postpartum. RESULTS: The greatest number of pregnant, active duty service women were found among ages 18-24 years, White race, Army service, junior enlisted rank, married status, and with no mental health diagnosis. Overall, over 50% of women in normal and preeclamptic pregnancies returned to their baseline BMI postpartum. Women in both populations more often gained than lost weight postpartum. Preeclampsia strongly affected weight retention, with 40.77% of overweight women and 5.33% of normal weight women progressing to postpartum obesity, versus 32.95% of overweight women and 2.61% of normal weight women in the main population. Mental health conditions were not associated with significant weight gain or PPWR. Women with cesarean deliveries gained more weight during pregnancy, had more PPWR, and lost more weight from third trimester to 6 months postpartum. CONCLUSIONS: Most women remain in their baseline BMI category postpartum, suggesting that prepregnancy weight management is an opportunity to reduce excess PPWR. Other opportunities lie in readiness-focused weight management during prenatal visits and postpartum, especially for patients with preeclampsia and cesarean sections. However, concerns about weight management for readiness must be carefully balanced against the health of the individual service members.