Accidental natalizumab administration to the third trimester of pregnancy in an adolescent patient with multiple sclerosis

Background: Natalizumab is neither licensed for the use in adolescents nor during pregnancy. There are no reports of accidental natalizumab exposure during pregnancy continued as long as to the third trimester of pregnancy. Aims: We report the outcome of pregnancy in a 17-year-old adolescent patient with multiple sclerosis (MS) treated with natalizumab from the age of 16, who was diagnosed to be pregnant in the 31st gestational week (gw) of pregnancy. To our knowledge, this report describes the first patient receiving natalizumab to the third trimester of pregnancy. Case report: Because of high relapse activity, natalizumab treatment was administered in an adolescent patient with MS. Pregnancy was diagnosed in the 31st gw after 17 natalizumab infusions, seven of them accidentally during pregnancy. Results: Pre- and postnatal development of the child was normal. Conclusions: The case reported indicates that accidentally continued natalizumab treatment until few weeks before delivery may have no negative impact on the developing foetus.