Multivariable modeling: A retrospective cohort study exploring the impact of socioeconomic status and distance to a rural academic center on all-cause preterm delivery.

Objective: Hospital-based labor and delivery units are closing at increasing rates in the rural US, significantly impacting maternal and newborn health. The objective of this study to determine if rurality-measured as distance from the hospital-and socioeconomic status-measured as insurance payor-impact both spontaneous and medically indicated preterm birth incidence at a single rural academic institution.

Methods: This was a retrospective cohort study using electronic medical records of patients with singleton pregnancies delivering at a single rural academic institution between 2016-2018. The primary outcome was preterm delivery (PTD) and secondary outcomes included low birth weight (LBW) and intensive care nursery (ICN) admission. The primary exposures included (1) travel time from a patient's address to the hospital and (2) insurance carrier as a proxy for socioeconomic status. Bivariate analyses indicated that travel time, insurance status, race, ethnicity, marital status, number of prenatal visits, gravida and para, and smoking status were significant predictors of all outcomes (LBW, ICN admission, and PTD). Therefore, these predictors were included in the multivariable logistic models.

Results: Within the multivariable logistic model, patients traveling 1-1.5 hours had approximately twice the odds of PTD (Odds Ratio, OR: 2.08, 95% Confidence Interval CI, 1.32, 3.29, p = .002), birth of a LBW neonate (OR: 2.15; 95% CI: 1.29-3.58, p = .005), and infant admission to the ICN (OR 1.83, 95% CI: 1.22-2.76, p = .004) compared to patients traveling under 30 minutes,. Insurance carrier status was not associated with increased odds of PTD, LBW, or ICN admission.

Conclusion: Patients living 1-to-1.5 hours from the hospital had an increased risk for LBW, ICN admission, and PTD, despite living in zip codes with less social deprivation than zip codes further away from the hospital.