For a study, researchers sought to assess disease activity, as well as the frequency and severity of flares, in pregnant and nonpregnant systemic lupus erythematosus (SLE) patients. The medical records of pregnant patients with SLE who were visited between January 1993 and June 2017 were examined. SLE controls who were not pregnant were matched based on age at diagnosis and illness duration prior to pregnancy. The cSLEDAI (clinical Systemic Lupus Erythematosus Disease Activity Index) and the Safety of Estrogens in Lupus Erythematosus National Assessment–SLEDAI Flare Index were used to measure systemic lupus erythematosus disease activity and flares, respectively. Disease activity was tracked from 6 months from conception until the postpartum period. For statistical analysis, the repeated measures mixed model, Cox regression, and cumulative hazard maps were utilized. 

In 77 patients, 90 pregnancies occurred. The cSLEDAI scores from 6 months until the postpartum period were comparable between the pregnant and control groups, while the controls were marginally but substantially higher at conception (mean +SEM, 3.57+0.45 vs 1.90 +0.36; P=0.019). When compared to controls, the pregnancy group had no significantly higher incidence of flare (41.11% vs 28.89%, P=0.086 and 7.78% vs 11.11%, P=0.445, respectively) or flare category (severe flare) (75.68% vs 53.85%, P=0.070 and 85.71% vs 70.00%, P=0.603, respectively). The flare incidence rate (95% CI)/100 patient-months in the pregnant and control groups was 6.75 (4.89–9.32) and 4.34 (2.96–6.38), respectively, resulting in an adjusted risk for flare (95% CI) of 1.54 (0.91–2.61) (P=0.110). 

When pregnant patients with SLE were compared to their appropriately matched nonpregnant SLE controls, there was no overall significant increase in SLE disease activity, flare incidence, or flare severity.