Outcomes of pregnancies complicated by maternal autoimmune diseases in Denmark, Finland, and Sweden: a multi-national population‐based register study

Background Maternal autoimmune diseases, including Sjögren’s disease (SjD), systemic lupus erythematosus (SLE), rheumatoid arthritis (RA), idiopathic inflammatory myopathies (IIM), and mixed connective tissue disease (MCTD), are associated with adverse pregnancy outcomes. However, comprehensive population-based studies evaluating the impact of these diseases across multiple countries are limited. Objective To characterize outcomes in pregnancies complicated by SjD, SLE, RA, IIM, and/or MCTD in Denmark, Finland, and Sweden. Study Design A population-based cohort study was conducted using data from national health registers from Denmark (1995–2017), Finland (2000–2022), and Sweden (2000–2021). The study included singleton pregnancies in women aged ≥15 years at delivery and with any of the five specified autoimmune diseases diagnosed before or during pregnancy, or within one year postpartum. Maternal demographics and complications, birth outcomes, neonatal characteristics, and long-term outcomes in children were described. Results The present study included 20,425 singleton pregnancies complicated by maternal SjD (n=1,913), SLE (n=3,570), RA (n=13,328), IIM (n=1,078), or MCTD (n=536). Across the three countries, common pregnancy complications included preeclampsia and preterm premature rupture of membranes, which occurred in 2–12%, and 1–16% of pregnancies, respectively; fetal growth restriction was reported in 3–11% of pregnancies complicated by SjD, SLE, RA, or MCTD. Emergency caesarean section was performed in 10–21% of all pregnancies. A total of 20,304 liveborn children were identified, of which 6–18% were preterm and 5–24% were small for gestational age. Neonatal unit admission rate varied between 9 and 24%. Second/third-degree atrioventricular block was reported in 1.5% and 0.9% of SjD pregnancies in Sweden and Finland, respectively. Conclusion The study provides a comprehensive overview of outcomes in pregnancies complicated by autoimmune diseases in three Nordic countries. These pregnancies show notable proportions of adverse maternal and neonatal outcomes, underscoring the importance of tailored clinical management and specialized perinatal care to address the unique challenges faced by the mothers and their children.