Editorial: ustekinumab during pregnancy—reassuring but still not enough. Authors' reply

Flare of IBD during pregnancy is associated with unfavourable pregnancy outcomes including increased risk of spontaneous abortion, prematurity and low birth weight.1 Consequently, current recommendations advise to continue IBD medication during pregnancy.2 However, the most significant concern of women with IBD regards the safety of medicines during pregnancy and their possible effects on the foetus. Most IBD drugs are considered of low risk during pregnancy and, so far, no increase in congenital malformations has been reported.3 IgG monoclonal antibodies are large molecules; hence, they do not actively cross the placenta during the first half of pregnancy but do transfer during the second half by binding the FcRn of the foetus. For example, infliximab levels have been detected in cord blood and in infants of women treated during pregnancy. Indeed, most data are regarding antiTNF agents, with no evidence of congenital anomalies or adverse effects on the development of newborn's immune system.4 Data regarding the safety of ustekinumab, a humanised IgG monoclonal antibody, during pregnancy are scarce and eagerly anticipated. Ours was the first prospective controlled study to date to summarise the outcomes of 27 pregnancies while on ustekinumab.5 We agree with the editorial comment concerning the small number of pregnancies in our cohort. However, our data are encouraging, especially since we compared pregnancies on ustekinumab to two different control groups, with similar outcomes in each group. Moreover, we have since expanded our database to 42 pregnancies with exposure to ustekinumab— with no adverse events reported. Additionally, and in contrast to realworld studies, prospective studies aimed to examine biologic agents in pregnant women with IBD are usually limited in sample size. Nevertheless, there is a need for large prospective, controlled studies to learn more on the potential effects of ustekinumab on newborn infants and on any shortand longterm impact on their development and their immune system.