Pregnancy outcomes in women with idiopathic inflammatory myopathies: a single-centre study from Sweden

To assess pregnancy and delivery outcomes in women with idiopathic inflammatory myopathies (IIMs) before and after diagnosis, in relation to maternal and IIM characteristics.

We identified women with IIM aged 18-40 years diagnosed at Karolinska University Hospital, and included in the Swedish nationwide myositis register (SweMyoNet) 2006-2022. Clinical data before and during pregnancy, and pregnancy and delivery outcomes were extracted from medical charts, and compared to background data of the Swedish general obstetric population during the same period.

We identified 34 births among 21 women during 2006-2021, classified into two groups: births occurring up to 5 years before (pre-IIM, n = 10) and births after IIM diagnosis (post-IIM, n = 24). We observed higher frequencies for all IIM births versus the general obstetric population: caesarean delivery (29% vs 21%), labour induction (27% vs 18%), and instrumental delivery (21% vs 9.1%). These outcomes were similarly frequent in pre- and post-IIM births. Conversely, the proportion of preterm births was lower in IIM births than in the general population (3.0% vs 5.6%). Overall, IIM disease activity was low at time of pregnancy according to Manual Muscle Test-8, creatinine kinase, and glucocorticoid doses.

Women with IIM, both before and after diagnosis, had higher proportions of labour induction, caesarean delivery, and instrumental delivery than the general population, regardless of low IIM disease activity at time of pregnancy. The increased proportions of these outcomes also in pre-IIM births may indicate an impact of pro-inflammation and autoimmunity on reproductive health before diagnosis.