Pregnancy Outcomes with Belimumab Save

Pregnancy in systemic lupus erythematosus (SLE) is fraught with problems of adverse pregnancy outcomes, more pregnancy loss and birth defects. Now a study of SLE pregnancies exposed to belimumab (BEL) shows and expected rate of pregnancy loss but a variable rate of birth defects.

Data were derived from the BEL clinical trials, the Belimumab Pregnancy Registry (BPR), and postmarketing/ spontaneous reports up to 8 March 2020.

Among pregnancies with BEL exposure, there were 319 pregnancies with known outcomes (excluding elective terminations), 223 (70%) of these ended in live births.  From the Live birth cohort, birth defects were identified in 5.6%) in belimumab-exposed pregnancies and 0/9 placeboexposed pregnancies.

The Belimumab Pregnancy Registry (BPR) , identified birth defects in 10/46 (21.7%) belimumab-exposed pregnancies in the BPR prospective cohort (enrolled prior to pregnancy outcome) and 0/4 belimumab-exposed pregnancies in the BPR retrospective cohort (enrolled after pregnancy outcome).  A similarly low birth defect rate (1/92; 1.1%) was found from postmarketing/spontaneous reports on BEL-exposed pregnancies.

There was no consistent pattern of birth defects across these datasets.

Pregnancy loss (excluding elective terminations) was reported in:

• Clinical Trial Data: 31.8% of belimumab-exposed women (vs 43.8% in a small placebo-exposed cohort) in clinical trials;
• BPR: 4.2% (2/48) of women in the BPR prospective cohort and 50% (4/8) in the BPR retrospective cohort;
• Post-marketing spontaneous reports: 31.4% (43/137) of belimumab-exposed women

As expected these SLE women were exposed to other drugs and confounders that muddy these interpretations. 

This is the largest descriptive summary of birth defects and pregnancy losses among women exposed to belimumab during pregnancy. It is unknown if the high rate of birth defects in the prospective BPR cohort is an outlier due to a small sample size, enrollment bias towards higher risk patients or a potential BEL related adverse event.