POS1424 PREGNANCY COURSE IN A COHORT OF WOMEN WITH MYOSITIS - RESULTS FROM REVNATUS

Background: Myositis is a rare autoimmune disease characterized by proximal and symmetrical muscle weakness and inflammatory infiltrates on muscle biopsy, and may affect women in reproductive age. Only few reports exist on pregnancy outcomes in women with myositis. Well-controlled disease at time of conception seems to give better outcome for the mother and the fetus (1). Inflammatory active disease before and during pregnancy has been associated with preterm birth and infant small for gestational age (1). Objectives: To describe the course of pregnancy in patients with myositis. Methods: We prospectively collected data on pregnancy in women with myositis in the nationwide Norwegian quality registry - RevNatus. ICD-10 codes: ICD-10 M33.0 (5), M33.1 (2), M33.2 (1), M33.9 (3). Eleven pregnancies in ten women with a known pregnancy outcome from 2016 – 2020 were included. Results: Median disease duration was 10 years (range 3-26), and median age at conception was 29 years (range 25-43). Five women had juvenile myositis. Two pregnancies ended in spontaneous abortions, one in 1st trimester and one in 2nd trimester. Nine pregnancies ended with live birth at median pregnancy week 39 (range 35-41) and a median birth weight of 3355 gram (range 2580-4750). None of the women experienced preeclampsia or HELLP. Three women was positive for ANA. Median CRP in second trimester was three (range 0-7). Among nine women with live births, seven were in remission, and two women had persistent disease in second trimester, defined by rheumatologist. Seven women used DMARDs in pregnancy, and two women used prednisolone 5 mg throughout pregnancy. Conclusion: We did not observe disease flare during pregnancy and no serious adverse outcomes in the pregnancies ending with live births. However, data are sparse, and larger cohorts are necessary to evaluate possible risk factors. References: 1. Munira S, Christopher-Stine L. Pregnancy in myositis and scleroderma. Best Pract Res Clin Obstet Gynaecol. 2020 Apr;64:59-67. doi: 10.1016/j.bpobgyn.2019.10.004. Epub 2019 Oct 18. PMID: 31928915. Disclosure of Interests: None declared