Objective Prior studies found conflicting results about whether lupus is likely to flare during or after pregnancy. Using a large cohort of pregnant and non-pregnant women with lupus, we estimated the effect of pregnancy on disease flares in systemic lupus erythematosus.

Methods Data were collected in the Hopkins Lupus Cohort 1987–2015. Women aged 14–45 years with >1 measurement of disease activity were included. The time-varying exposures were classified as pregnancy, postpartum or non-pregnant/non-postpartum periods. Flares were defined as: (1) change in Physician Global Assessment (PGA)≥1 from previous visit and (2) change in Safety of Estrogens in Lupus National Assessment-Systemic Lupus Erythematosus Disease Activity Index (SELENA-SLEDAI)≥4 from previous visit. A stratified Cox model estimated HRs with bootstrap 95% CIs.

Results There were 1349 patients, including 398 pregnancies in 304 patients. There was an increased rate of flare defined by PGA during pregnancy (HR: 1.59; 95% CI 1.27 to 1.96); however, this effect was modified by hydroxychloroquine (HCQ) use, with the HR of flares in pregnancy compared with non-pregnant/non-postpartum periods estimated to be 1.83 (95% CI 1.34 to 2.45) for patients with no HCQ use and 1.26 (95% CI 0.88 to 1.69) for patients with HCQ use. The risk of flare was similarly elevated among non-HCQ users in the 3 months postpartum, but not for women taking HCQ after delivery.

Conclusions Our study supports and extends previous findings that the incidence of flare is increased during pregnancy and within the 3 months postpartum. Continuing HCQ, however, appeared to mitigate the risk of flare during and after pregnancy.