ObjectivesAdverse pregnancy outcomes (APOs) are more common among women with SLE compared to the general population and the underlying immunopathological mechanisms are largely unknown. The type I interferon (IFN) signature persists in complicated SLE pregnancies, while it is downregulated in uncomplicated SLE pregnancies. Moreover, IFNα protein concentrations are higher in SLE compared to healthy pregnancies, but whether IFNα protein levels are associated with APOs in SLE is unknown. The aim of this study was to evaluate whether APOs are more common in Swedish women with SLE compared to healthy controls, and if this associates with circulating IFNα protein or autoantibodies.MethodsWe included 83 births from 77 women with SLE and 58 births from 58 healthy controls (HC). Repeated peripheral blood samples were collected and IFNα protein levels were quantified with Simoa. Anti-nuclear antibody (ANA) specificities and anti-phospholipid antibodies (aPL) during pregnancy was analysed using multiplexed bead technology. APOs were defined as an infant small for gestational age (SGA), preterm birth, low birth weight (LBW) and/or preeclampsia. Multivariate orthogonal partial least squares analysis (OPLS) was used to examine SGA, LBW and/or preterm (combined outcomes, Y-variable) in relation to mean IFNα protein level, IFNα positivity, ANA specificity and aPL positivity during pregnancy.ResultsAPOs were more common in women with SLE compared to healthy women (33% compared to 12%, p=0.005). The most common outcome was SGA, which was present in 17% of women with SLE compared to 3% of HC (p=0.01). In OPLS, SGA, LWB and/or preterm birth was most positively associated to mean IFNα protein level and IFNα positivity in plasma during pregnancy. Preeclampsia was unrelated to IFNα and autoantibody positivity in women with SLE. In univariate analysis, the mean IFNα protein level was significantly higher in women with SLE who had an infant who was SGA, LBW and/or preterm compared to women without these APOs.ConclusionIFNα protein level in plasma is a potential risk factor for giving birth to an infant who is small for gestational age, has low birth weight and/or is delivered preterm in SLE.