Abstract
OBJECTIVES: The purpose of this study was to evaluate the effect of high SES on multiple pregnancy outcomes, while controlling for confounding factors. METHODS: Using the Healthcare Cost and Utilization Project Nationwide Inpatient Sample (HCUP-NIS), the largest American medical database including 20 % of annual hospital admissions, we studied the years 2004-2014 inclusively. We conducted a population-based retrospective cohort study consisting of women from different median household income quartiles throughout the United States. Women in the highest household income quartile were compared to those in all other lower income quartiles combined. Chi-square and Fischer exact tests were used to compare demographic and baseline characteristics. Univariate and multivariate regression analyses were carried to adjust for confounding factors, including ethnicity, pre-existing conditions, smoking status, obesity, illicit drug use and insurance type. RESULTS: Among 5,448,255 deliveries during the study period with income data, 1,218,989 deliveries were to women from the wealthiest median household income. These women were more likely to be older, Caucasian, and have private medical insurance (P < 0.05, all). They were less likely to smoke, have chronic hypertension, pre-gestational diabetes, and use illicit drugs (P < 0.05, all). They were less likely to develop complications including gestational hypertension (aOR 0.87 95 %CI 0.85-0.88), preeclampsia (aOR 0.88 95 %CI 0.86-0.89), eclampsia (aOR 0.81 95 %CI 0.66-0.99), gestational diabetes (aOR 0.91 95 %CI 0.89-0.92), preterm premature rupture of membranes (PPROM) (aOR 0.92 95 %CI 0.88-0.96), preterm birth (aOR 0.90 95 %CI 0.89-0.92), and placental abruption (aOR 0.89 95 %CI 0.85-0.93). They were less likely to have an intra-uterine fetal death (IUFD) (aOR 0.80 95 %CI 0.74-0.86), but more likely to deliver neonates with congenital anomalies (aOR 1.10 95 %CI 1.04-1.20). CONCLUSIONS: Higher SES predisposes to better pregnancy outcomes, even when controlled for confounding factors such as ethnicity and underlying baseline health status. Efforts are required in order to eliminate health disparities in pregnancy.