Discontinuing natalizumab during the first trimester of pregnancy increased relapse risk during pregnancy and postpartum. Continuing natalizumab after the 30th gestational week significantly reduced postpartum relapse risk, but also increased anemia in newborns.


Prior smaller studies have shown that exposure to natalizumab during the first trimester of pregnancy does not seem to pose a major teratogenic risk. However, exposure all through pregnancy was associated with hematological abnormalities in newborns. A prospective, observational cohort study assessed relapses during pregnancy and postpartum as well as pregnancy outcomes, including fetal hematological abnormalities, in women with highly active MS who used natalizumab. Patients were divided into 2 groups: those who terminated natalizumab during the first trimester (1 Trim-group) or after the first trimester (>1 Trim-group). Prof. Sandra Thiel (Ruhr University Bochum, Germany) presented the results [1].

Included were 350 pregnant women, 171 in the 1 Trim-group and 179 in the >1 Trim-group. The latter group stopped natalizumab after a median of 31 gestational weeks (range 12.1–39.7). Women in the >1 Trim-group had significantly fewer relapses during pregnancy (5.2% vs 32.4%; P<0.001) and postpartum (22.8% vs 49.7%; P<0.001) compared with the 1 Trim-group. Also, early restart (4 weeks postpartum) decreased relapse risk postpartum (OR 0.32; 95% CI 0.17–0.58; P<0.001).

Pregnancy outcomes were similar between groups. In the >1 Trim group and the 1 Trim group, 12.9% and 10.6% of births were preterm (P=0.625), while 4.7% and 3.4% of newborns had congenital abnormalities (P=0.719). In both groups, newborns were smaller than expected. To assess anemia and thrombocytopenia in 122 newborns with available blood counts, the >1 Trim group was stratified into women who stopped natalizumab after gestational week 30 (>30GW; n=79) and before week 30 (<30GW; n = 43). Compared with the <30GW group, newborns in the >30GW group had significantly more often hematological abnormalities (57% vs 39.5%; P=0.10). Rates of anemia were 46.8% and 27.9%, respectively; rates of thrombocytopenia were 22.8% and 16.3%. Significantly more women in the <30GW group suffered from relapse (38.5% vs 16%), especially during the first postpartum trimester.

“These study results should lead to a risk-benefit discussion between women treated with natalizumab and their neurologists, to continue treatment up to week 30 or even week 34 of gestation, in combination with an early restart during the first 4 weeks after delivery,” concluded Prof. Thiel

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