Obesity as an amplifier of peripartum cardiovascular risk in women with rheumatoid arthritis

Background Rheumatoid arthritis (RA) and obesity each independently increase peripartum cardiovascular risk through chronic inflammation, endothelial dysfunction, and metabolic dysregulation. Obesity prevalence among patients has risen to 11% nationally, while RA prevalence at delivery nearly doubled from 0.12% to 0.17% between 2016 and 2021. Whether obesity amplifies RA-associated peripartum cardiovascular complications beyond additive risk remains unknown. Methods We conducted a retrospective cross-sectional study using the 2016–2022 National Inpatient Sample (NIS) databases, incorporating 5,338,276 delivery hospitalizations representing 26.7 million weighted discharges. Four mutually exclusive exposure groups were constructed: (1) No RA/No Obesity [reference], (2) RA only, (3) Obesity only, (4) RA+Obesity. Primary outcome: preeclampsia/eclampsia. Secondary outcomes: peripartum cardiomyopathy (PPCM), cardiac arrhythmias, AKI, stroke, VTE, heart failure, and composite. Survey-weighted multivariable logistic regression adjusted for age, race, insurance, income quartile, Charlson index, chronic hypertension, diabetes, GDM, dyslipidemia, CKD, CAD, PCOS, smoking, multiple gestation, cesarean delivery, teaching status, region, hospital size, and year. Results Unadjusted preeclampsia rates increased across the exposure gradient: 5.99% (reference), 8.67% (RA only), 13.98% (Obesity only), and 16.57% (RA+Obesity). In fully adjusted models (reference: No RA/No Obesity), obesity alone carried aOR=1.79 (95%CI 1.77–1.81, p<0.001) and RA+Obesity aOR=1.68 (95%CI 1.40–2.01, p<0.001) for preeclampsia; RA alone was non-significant (aOR=1.08, p=0.088), attenuated by chronic hypertension and metabolic comorbidities. For composite CV outcomes, RA+Obesity showed aOR=1.38 (95%CI 1.15–1.65, p<0.001) vs. reference. The RA×Obesity multiplicative interaction term was non-significant for preeclampsia (OR=0.87, p=0.163), but was statistically sub-multiplicative for composite CV outcomes (OR=0.79, p=0.020). PPCM was absent in the RA+Obesity group (zero events). After excluding chronic hypertension, RA became an independent predictor of preeclampsia (aOR=1.11, p=0.039), confirming HTN as a key confounding pathway. Conclusion In this national cohort of 26.7 million deliveries, obesity, not RA, was the predominant determinant of peripartum cardiovascular complications. Women with concurrent RA and obesity exhibited markedly higher risks of preeclampsia and composite cardiovascular morbidity, though without synergistic interaction. The concurrent rise in preeclampsia (5.2% to 8.3%) and doubling of RA-obesity co-prevalence highlight a growing cardio-obstetric risk population. As biologic therapies enable more pregnancies in women with RA, targeted preconception weight management and intensified blood pressure surveillance are warranted to mitigate adverse outcomes.