Pregnancy outcomes in idiopathic inflammatory myopathies: a Portuguese multicentre study.

Introduction: Idiopathic inflammatory myopathies (IIM) are rare autoimmune diseases that may complicate pregnancy, but evidence remains scarce. Disease activity at conception and during gestation, together with autoantibody profiles, are considered major determinants of adverse pregnancy outcomes (APOs). Methods: We conducted a retrospective multicentre study of 12 pregnancies in 10 women with IIM followed at four Portuguese tertiary centers (2009-2025). Demographic, clinical, immunological, therapeutic, maternal, and perinatal data were collected from medical records. Disease activity was assessed by clinical features, laboratory data, modified skin Disease Activity Score, and Manual Muscle Testing-8. Results: Phenotypes included overlap myositis (n = 4), antisynthetase syndrome (n = 3), dermatomyositis (n = 3), immune-mediated necrotising myopathy (n = 1), and polymyositis (n = 1). Myositis-specific/associated autoantibodies were detected in 91.7% of the cases, most frequently anti-Ro52 and anti-Jo-1. Disease remission at conception was documented in nine pregnancies (75.0%). Overall, APOs occurred in six pregnancies (50.0%): four miscarriages, one stillbirth, and one fetal growth restriction (FGR) with a small-for-gestational-age neonate. Of the 12 pregnancies, seven resulted in live births. All APOs occurred in pregnancies with disease flares, none occurred when disease remained stable. Among pregnancies with known preconception status, APOs occurred both in pregnancies conceived under active disease and in some conceived during remission. The most severe outcomes (stillbirth, FGR) occurred in one mother with antisynthetase syndrome and markedly elevated anti-Jo-1 titres. No cases of preeclampsia, eclampsia, congenital anomalies, or neonatal lupus were observed. Discussion: In this cohort, APOs were frequent, particularly among pregnancies complicated by disease activity. Although remission at conception was common, it did not fully prevent flares or obstetric complications. Anti-Jo-1 positivity appeared to cluster among the more severe cases, suggesting potential clinical relevance for monitoring. Multidisciplinary care and preconception optimization remain essential. Larger multicentre registries will be crucial to improving understanding and management of pregnancy in IIM.