All of the mothers treated with natalizumab during late pregnancy had experienced serious natalizumab-withdrawal relapses either prior to or during pregnancy.
The authors note that the haematological abnormalities resolved during the 4 months after birth and none of the infants needed any specific treatment, although one subclinical bleeding complication was reported. Detectable cord blood levels of natalizumab were found in all 5 infants tested. In general, the concentrations were higher in those exposed closer to the time of delivery and with more frequent late-pregnancy exposures. This is consistent with normal placental immunoglobulin transport mechanisms. One malformation was reported (atrioventricular septal defect); however the infant was also exposed to valproate throughout pregnancy.
These observations are limited by the small sample size, and there are no long-term developmental outcomes for most of the children. The authors say however that their findings are useful for therapeutic decisions in women with similarly severe disease activity.
A summary produced by the UK Teratology Information Service (UKTIS) in October 2011 notes that there are currently insufficient data to enable assessment of the safety of natalizumab use during pregnancy. Due to the limited experience of its use during pregnancy, data investigating both the risk of PML development amongst pregnant patients, and the risk of viral transmission to the foetus are currently unavailable.
The summary recommends that where natalizumab is required during pregnancy, close monitoring of maternal neurological function is advised. Should maternal symptoms of PML present during pregnancy, enhanced foetal and neonatal monitoring may also be warranted.
The manufacturer recommends that it should not be used during pregnancy unless the clinical condition of the women requires treatment with natalizumab. If a woman becomes pregnant while taking it, discontinuation should be considered.