Objectives Exploring the associations between disease activity and medications with offspring birth weight, pre-eclampsia and preterm birth in systemic lupus erythematosus (SLE).

Methods Data from the Medical Birth Registry of Norway (MBRN) were linked with data from RevNatus, a nationwide observational register recruiting women with inflammatory rheumatic diseases. Singleton births in women with SLE included in RevNatus 2006–2015 were cases (n=180). All other singleton births registered in MBRN during this time (n=498 849) served as population controls. Z-score for birth weight adjusted for gestational age and gender was calculated. Disease activity was assessed using Lupus Activity Index in Pregnancy. We compared z-scores for birth weight, pre-eclampsia and preterm birth in cases with inactive disease, cases with active disease and population controls.

Results Z-scores for birth weight in offspring were lower in inactive (−0.64) and active (−0.53) diseases than population controls (−0.11). Inactive disease did not predict pre-eclampsia while active disease yielded OR 5.33 and OR 3.38 compared with population controls and inactive disease, respectively. Preterm birth occurred more often in inactive (OR 2.57) and active (OR 8.66) diseases compared with population controls, and in active compared with inactive disease (OR 3.36).

Conclusions SLE has an increased odds for low birth weight and preterm birth, amplified by active disease. The odds for pre-eclampsia is elevated in active, but not inactive disease. This calls for tight follow-up targeting inactive disease before and throughout pregnancy.