Variable Pregnancy Outcomes with Belimumab in SLE Save

An analysis of the belimumab clinical trials, the Belimumab Pregnancy Registry (BPR), and postmarketing/spontaneous reports looked at outcomes in pregnant systemic lupus erythematosus (SLE) exposed to belimumab reported there are few pregnancies and confounding disease and comorbidity factors to provide clear guidance for such patients. 

A total of 319 BEL-exposed pregnancies with known outcomes (excluding elective terminations) were included. They identified: 

• Live births = 223
• Birth defects in 4/72 (5.6%) among BEL-exposed and 0/9 placebo-exposed pregnancies in 18 clinical trials,
  • 10/46 (21.7%) BEL-exposed in the BPR prospective cohort and 0/4 belimumab-exposed pregnancies in the BPR retrospective cohort (enrolled after pregnancy outcome), and
  • 1/92 (1.1%) in BEL-exposed from postmarketing/spontaneous reports.
  • No consistent pattern of birth defects across datasets.
• Pregnancy loss in 31.8% (35/110) in BEL-exposed and 43.8% (7/16) of placebo-exposed women in clinical trials
  • 4.2% (2/48) of women in the BPR prospective cohort and 50% (4/8) in the BPR retrospective cohort;
  • 31.4% (43/137) in postmarketing/spontaneous reports.

Variance in outcomes in these different datasets primarily more uncertainty than confidence to the limited data published thus far on pregnancy outcomes following belimumab exposure. Clearly these results are confounded by entry criteria differences, background SLE activity/drugs and comorbidities and non-uniformity of pregnancy reporting outcomes in these different datasets. While the risk of birth defects with BEL exposure was low in clinical trials (5.6%) and post marketing reports (1.1%)the higher rate (21.7%) seen in the BPR (registry) appears to reflect an inclusion bias but will need to be further studied.