We did, however, observe a larger percentage of patients using certolizumab pegol at inclusion in our cohort (21.2%) than one can expect from the usual Dutch RA patient population.22 This could be caused by a switch to certolizumab pegol already before referral to our specialised clinic, since literature shows no to minimal placental transfer of certolizumab pegol during pregnancy.23 During pregnancy, TNF inhibitors were stopped at the gestational age advised by the EULAR. The gene discussed is TNF; the disease is rheumatoid arthritis.