Reply

To the Editor: We thank the authors for their interest in our recent article 1 and for highlighting the potential role of endometriosis in pregnancies among patients with systemic lupus erythematosus (SLE). We agree that endometriosis is an important clinical condition characterized by immune dysregulation and inflammatory pathways that may overlap with autoimmune diseases, including SLE. The possibility that coexisting endometriosis could influence pregnancy outcomes in this population is a clinically relevant consideration. As noted by the authors, prior research has suggested that endometriosis may be associated with SLE2, 3 and with adverse pregnancy outcomes (APOs), 4 and emerging literature indicates shared biologic mechanisms between endometriosis and SLE. 5 Increased awareness of coexisting conditions is important for clinicians caring for pregnant patients with SLE, particularly given the complexity of managing risks in this high‐risk population. Our study was designed as a nationwide descriptive analysis aimed at characterizing temporal trends in APOs and treatment patterns among pregnant patients with SLE in Sweden over two decades, rather than evaluating etiologic contributions of specific comorbidities. 1 The primary objective was to assess whether the burden of APOs has changed over time at the population level and to contextualize these trends alongside evolving treatment practices. We focused on the overall population and several selected clinical subgroups with established and well‐documented associations with APO risk in SLE, such as antiphospholipid syndrome and lupus nephritis. Evaluation of additional coexisting gynecologic conditions, including endometriosis, was beyond the scope of the present analyses. In response to the authors’ interest in endometriosis, we searched for a history of endometriosis before pregnancy in our cohort and observed a low prevalence; 17 of 1,417 (1.2%) SLE pregnancies in which the woman had a history of endometriosis before pregnancy. Given these small numbers, particularly when further stratified across calendar periods, meaningful temporal trend analyses of the subgroup with endometriosis would not have been statistically reliable. In addition, because our study population was restricted to pregnancies that led to delivery, it was not designed to evaluate the broader reproductive implications of endometriosis in SLE, such as fertility challenges or the need for assisted reproductive treatments. Importantly, the observed decline in APO proportions over time in our study is unlikely to be explained solely by unmeasured comorbidities unless their prevalence changed substantially during the study period. Future research starting from patients with SLE and coexisting endometriosis, rather than pregnancies alone, may provide additional insight into reproductive trajectories, including fertility treatment use and pregnancy outcomes. Such studies could help refine risk stratification and guide multidisciplinary management strategies. We appreciate the authors’ emphasis on increased clinical vigilance and the need for continued investigation into factors that may contribute to pregnancy risk in patients with SLE. Their comments highlight an important area for future research, and we hope that our findings contribute to ongoing efforts to improve care and outcomes for this population. Supporting information References - 1. Nguyen NV, Sandström A, Dominicus A, Svenungsson E, Hellgren K, Simard JF, et al. Nationwide temporal trends in adverse pregnancy outcomes and treatments in systemic lupus erythematosus pregnancy over two decades in Sweden. Arthritis Rheumatol 2026;78(8):1700–1709. doi: 10.1002/art.70018 [DOI] [PMC free article] [PubMed] [Google Scholar] - 2. Harris HR, Simard JF, Arkema EV. Endometriosis and systemic lupus erythematosus: a population‐based case–control study. Lupus 2016;25(9):1045–1049. doi: 10.1177/0961203316631635 [DOI] [PMC free article] [PubMed] [Google Scholar] - 3. Sun YH, Leong PY, Huang JY, et al. Increased risk of being diagnosed with endometriosis in patients with systemic lupus erythematosus: a population‐based cohort study in Taiwan. Sci Rep 2022;12(1):13336. doi: 10.1038/s41598-022-17343-4 [DOI] [PMC free article] [PubMed] [Google Scholar] - 4. Farland LV, Prescott J, Sasamoto N, et al. Endometriosis and risk of adverse pregnancy outcomes. Obstet Gynecol 2019;134(3):527–536. doi: 10.1097/AOG.0000000000003410 [DOI] [PMC free article] [PubMed] [Google Scholar] - 5. Zervou MI, Tarlatzi TB, Grimbizis GF, et al. Co‐occurrence of endometriosis with systemic lupus erythematosus: genetic aspects. Int J Mol Sci 2025;26(14):6841. doi: 10.3390/ijms26146841 [DOI] [PMC free article] [PubMed] [Google Scholar] Associated Data This section collects any data citations, data availability statements, or supplementary materials included in this article.