ObjectiveTo compare obstetric/birth outcomes and rehospitalization among women with and without rheumatoid arthritis (RA) or systemic lupus erythematosus (SLE) and their infants.MethodsThis population‐based retrospective cohort study identified women with RA (n = 1,223) and SLE (n = 1,354) and unexposed women with singleton births 1987–2014 in Washington State in linked vital hospital discharge records. Outcomes, including cause‐specific hospitalizations <2 years postpartum, were compared by estimating adjusted relative risks (RRs) and cause‐specific rehospitalization hazard ratios (HRs) with 95% confidence intervals (95% CIs).ResultsWe observed increased risks of several adverse outcomes; RRs were often greatest for SLE. Women with RA/SLE more often required rehospitalization, most notably at <6 months postpartum (RA: 4% versus 2%; RR 2.22 [95% CI 1.62–3.04]; SLE: 6% versus 2%; RR 2.78 [95% CI 2.15–3.59]). Maternal postpartum rehospitalization was greatest for musculoskeletal conditions (RA: HR 19.1 [95% CI 13.6–26.8]; SLE: HR 29.8 [95% CI 22.1–40.1]). Infants of women with SLE more often had malformations (9% versus 6%; RR 1.46 [95% CI 1.21–1.75]), and increased mortality at <2 years (RR 2.11 [95% CI 1.21–3.67]). Infants of women with SLE also experienced more frequent rehospitalizations in their first year of life.ConclusionWomen with RA or SLE and their infants experienced adverse outcomes, particularly infants of women with SLE. Maternal/infant rehospitalization was more common; most marked in the early months postpartum. Close follow‐up during these time periods is crucial to minimize adverse outcomes.