A recent report from the Belimumab Pregnancy Registry (NCT01532310) analysed available data on the consequences of belimumab (BEL) use in pregnant women with systemic lupus erythematosus (SLE).1 Although limited by multiple confounders and methodological differences, the study did not reveal an increased risk of birth defects or pregnancy losses among women treated with BEL.

Transplacental passage of BEL has been studied in cynomolgus macaques but not conclusively demonstrated to occur in humans.2 Thus, questions related to transplacental passage of BEL include: Does it occur in humans and to what extent? How long does it take until BEL is cleared post-partum?

Based on our previous report of immunologic changes observed at birth and during 7 months of follow-up in a child exposed prenatally to BEL,3 we have studied the transfer of BEL in this mother-and-child pair.

A 29-year-old woman with SLE from 2005 with arthritis and skin disease had a severe lupus flare during her first pregnancy in 2005–2006. She delivered at gestational …