Babies born to women who are treated with Tysabri (natalizumab) during pregnancy are more likely to develop abnormal blood cell counts if the treatment continues beyond week 30 of pregnancy.
Since more relapses occurred in women who quit the treatment before this time, researchers from the Ludwig Maximilian University of Munich in Germany concluded that 30 weeks was the optimal time interval to stop the treatment in pregnant women.
The data was shown at a presentation at the 7th Joint ECTRIMS-ACTRIMS Meeting in Paris, France, a gathering of more than 9,000 researchers at one of the largest MS-focused meetings in the world.
The risk of a drop in blood cell counts in babies born to mothers on Biogen’s Tysabri is a known effect, but it rarely has been studied in relationship to relapses among mothers who quit the treatment during pregnancy.
The study, “Long-term exposure to natalizumab during pregnancy – a prospective case series from the German Multiple Sclerosis and Pregnancy Registry,” turned to the German Multiple Sclerosis and Pregnancy Registry to determine if there was an optimal time to stop treatment with the drug.
The team identified 40 women treated with Tysabri, enrolled in the registry.
Among 32 babies in which blood cell counts were available upon birth, 15 had abnormally low cell counts. One-third was in the group of mothers who stopped treatment before week 24, and 39 percent were in the group who quit Tysabri before week 30.
Babies had either anemia — a lack of red blood cells — or a lack of platelets. Only one newborn received treatment for the condition.
Meanwhile, four women experienced relapses during pregnancy, of which three were in the group who quit Tysabri treatment before week 30.
Eight more women had relapses after delivering their babies, of which three were in the group who quit before week 24, and five in the group who quit before week 30.
Based on these data, researchers suggest that week 30 might be a good time to stop Tysabri treatment in pregnant women, for both the mother and the baby. However, in women with aggressive MS and higher disability, it may be necessary to continue the therapy beyond this time to reduce the risk for relapses.