Background: Maternal health care deserts (HCD) are defined as areas without a hospital or birth center offering obstetric care or areas without obstetric providers. These deserts comprise more than one third of all United States counties.1 Annually, over 400,000 births occur in these limited maternal healthcare regions. Increasing attention has been drawn to stationing of active-duty service members (ADSM) and their families in these areas with little to no obstetric health care. Studies show the incidence of preventable pregnancy outcomes (PPO) may be increased in HCD, where providers and medical resources are scarce. Inadequate access to care is frequently cited as a contributing factor in maternal and neonatal morbidity and mortality in the US.2 In addition to its impact on morbidity and mortality, scarce maternal care poses practical challenges including increased travel time to routine preventative appointments and emergency care, prolonged wait times for specialty care, and ultimately poor satisfaction with care.3 As the Defense Health Agency (DHA) has faced shortages in personnel, restrictions in budget, and reduced capacity, the nearly 10 million Military Health System (MHS) beneficiaries are increasingly reliant on referrals outside of Military Treatment Facilities to the TRICARE provider network.4 In some settings, the civilian healthcare sector may also lack the necessary resources to provide adequate care as more than half of armed forces bases in the US exist within healthcare deserts.5 In other markets, the decision to deprioritize obstetric care in the DHA run military treatment facilities may have the unintentional impact of overwhelming communities that are not able to support the patient load. This study is designed to assess the impact of US military base location in maternal HCD and how these limitations affect ADSM obstetric outcomes, long-term health, readiness, and retention. Methods: Using the Military Assessment and Readiness System (MARS) at Womack Army Medical Center, Fort Liberty, North Carolina, we identified pregnant female ADSMs from 2011 to 2021. We conducted survival analysis to assess the effect of social and community factors associated with HCDs on the risk of PPO. Factors associated with HCDs included distance between the patient’s residence and obstetric clinic, Center for Medicaid and Medicare Services (CMS) low-income designation of the patient’s residence and clinic location, as well as the Social Deprivation Index (SDI) for the clinic and patients’ residences.6 Our data were grouped into 5 SDI categories based on the overall SDI score: 1) 1-25 (Low SDI), 2) 26-50 (Middle Low), 3) 51-75 (Middle High), 4) 76-100 (High), and 5) no data. Collectively, these HCD related metrics were used to determine changes in the risk of PPO among pregnant ADSMs. Inclusion criteria for obstetric related outcomes included maternal suicide, postpartum hemorrhage, preterm delivery, cardiomyopathy and other cardiac conditions, maternal sepsis, venous thromboembolism, and eclampsia. Our analysis included demographic and military specific variables such as race, age, body mass index (BMI), service branch, marital status, education level, and rank/pay grade. Results and Discussion: Of the 545,851 female ADSMs that began military service between 2011 and 2021, there were 141,360 with an incident pregnancy for a rate of 259.0 incident pregnancies per 1,000 females. There were 21,544 pregnancies that resulted in PPO for a rate of 152.4 PPOs per 1,000 females. In the analysis, non-Hispanic White ADSM comprised 55.6% of our cohort. Survival analysis indicated that increased risk of PPO was associated with Asian/Pacific Islander race, younger age and lower rank, non-Air Force service, and increasing age, education, and BMI. There was no association between Hispanic ethnicity and PPO. The mean age of those with PPO was significantly lower than those ADSM without PPO (27.5 vs. 29.6; P<0.001). Mean BMI, however, was significantly higher in those with PPO (26.9 vs. 28.9; P<0.001). Pregnancy factors such as high-risk pregnancy (AHR = 1.59; 95% CI: 1.54,1.64) and having more than one newborn were also associated with increased PPO risk. The risk of PPO increased significantly based on distance between the place of residence and location of obstetric clinic. Risk increased with increasing distance between the clinic and patient residence. Importantly, the mean distance from the clinic to the residence of the patient, for those with a distance less than 100 miles, was significantly higher in those with PPO (10.6 vs. 11.8; P<0.001). Patients living 0 miles and 1 to 5 miles had the same PPO risk. However, as distance between clinic and residence increased, we observed that PPO risk increased. ADSM living between 6 and 40 miles from their clinic had a 30% increase in PPO risk (AHR = 1.30; 95% CI: 1.24,1.37; P<0.001) and those living between 41 and 100 miles from their maternal health care clinic had an 83% increase in PPO risk (AHR = 1.83; 95% CI: 1.68,2.00; P<0.001). Measurements beyond 100 miles were not entirely reliable (AHR = 1.01; 95% CI: 0.95,1.08). The SDI is a composite score including community-based population/demographic factors that increases as area deprivation increases. Including SDI enables our model to incorporate community-based factors associated with HCD, that are not otherwise captured. Previous studies have demonstrated that SDI is positively associated with poor access to health care and poor health outcomes. In our study, PPO risk also increased with increasing SDI of both the patient residence and the clinic location. Patients from higher SDI residences treated at low SDI clinics typically experienced higher PPO risk. Further, those treated at high SDI clinics, regardless of patient residence SDI, also typically experienced higher PPO risk. Risk increased by about 15% with clinic SDI and reached nearly 50% increase as patient residence SDI. Further, SDI interactions intensified the risk over 100% in some cases. Interactions between the SDI of the clinic and patient residence revealed some associations with increased PPO risk when compared to those in the lowest clinic and patient residence SDI group. Patients from higher SDI residences treated at low SDI clinics typically experienced higher PPO risk. Further, those treated at high SDI clinics, regardless of patient residence SDI, also typically experienced higher PPO risk. However, interestingly, those seen at a clinic with a lower-middle SDI, between 26 and 51, were typically at a decreased or null PPO risk regardless of the patient residence SDI. Additionally, we investigated low-income designation by the CMS and found this category was significantly associated with increased PPO risk, especially in cases where both the clinic and the patient residence were in a low-income location (AHR = 5.07; 95% CI: 4.86,5.28). A low-income clinic was associated with a higher risk increase (AHR = 4.33; 95% CI: 4.10,4.58) compared to a low-income patient residence (AHR = 3.47; 95% CI: 3.30,3.65). Conclusion: Income, clinic proximity, and SDI factors associated with health care deserts were all associated with increased risk of PPO in the ADSM population (2011-2021). Our study shows that the risk of PPO was higher among those living or being treated in low-income areas, those living or being treated in areas with higher SDI, and those living in areas that were further away from their treating clinic. Demographic factors associated with an increased PPO risk were an average age below 25 years of age, particularly less than 21, Asian or Pacific Islander race, junior enlisted or company grade officer rank, unmarried status, high BMI, diagnosis of high-risk pregnancy, and multiple gestation. These multidimensional findings suggest that increases in PPO are associated with characteristics indicative of HCDs. Our study highlights the importance of adequate staffing of military obstetric care facilities with prenatal care and labor and delivery units, and the necessity of access to this care for active-duty service members. We suggest further studies to better understand how these SDI effects on obstetric outcomes can be mitigated to protect long-term health, and retention of postpartum ADSM.