BACKGROUND: Pregnancy may have a beneficial effect on disease activity in rheumatoid arthritis (RA) but the evidence is more conflicting in spondyloarthritis (SpA). The aim of this study was to analyse disease activity and relapse during pregnancy in women with RA and SpA. METHODS: Consecutive pregnant women with RA or SpA were enrolled in this French multicentre observational cohort from 2014 to 2022. Women who had at least two prenatal visits (including one in the first trimester) were included in the analysis. Disease relapse was defined as treatment intensification (initiation or switch of a DMARD) or increase in disease activity scores (DAS28-CRP for RA patients
ASDAS-CRP and/or BASDAI for SpA patients). RESULTS: Of the 124 pregnant women included, 53 had RA and 71 had SpA. A total of 18 (35%) RA and 44 (62%) SPA received a TNF inhibitor during pregnancy. At the group level, disease activity indexes remained stable in the 1st, 2nd and 3rd trimesters. Disease relapse during pregnancy occurred in 17 (32%) RA patients and 28 (39%) SpA patients, among whom 30 (24%) requiring a treatment intensification. In multivariable analysis, factors associated with disease relapse were nulliparity (odds ratio, OR: 6.5, 95%CI: 1.1 to 37.9) and a disease flare in the 12 months prior to conception (OR: 8.2, 95%CI: 1.6 to 42.7) for RA patients, and a history of bDMARD use (OR: 5.4, 95%CI: 1.1 to 27.3) for SpA patients. CONCLUSION: Disease activity remained stable during pregnancy in women with RA and SpA but almost a quarter required major changes to their treatment.