Florence, Italy—Natalizumab was a welcome new option for multiple sclerosis (MS) patients who did not respond to or could not tolerate other treatments. How to manage the regimen during pregnancy can present a dilemma, however.

Natalizumab during pregnancy is the focus of two new studies published in the journal Neurology. Italian researchers associated with the MS Study Group of the Italian Neurological Society determined that women prescribed natalizumab for MS potentially experience increased disease activity if they stop taking it prior to pregnancy. They also found, however, that the risk might be reduced if the drug is used up until conception.

A second, related study cautions that using natalizumab during the first trimester might slightly increase the risk of miscarriage but reassures that the risk is small and within the risk range of miscarriage in the general population.

MS itself is not associated with a greater risk of birth defects, and pregnancy has no long-term effects on the disease process, according to background information in the article, which also points out that older medications, interferon betas, are generally considered to be safe during pregnancy.

Included in both studies were 92 pregnancies in 83 women taking natalizumab for relapsing-remitting MS. Participants were divided between those who stopped taking natalizumab before their last menstrual period and those who stopped taking the drug after their last period, with 75% of the pregnancies exposed to natalizumab for an average of just more than a week.

The 92 pregnancies resulted in 75 live births, and researchers followed up with the women every 6 months, as well as when they had a relapse, and 1 year after delivery.

The first study found that the relapse rate during pregnancy was three times higher in the 92 pregnancies compared to disease activity in 350 pregnancies in women with MS who either took no medication or who took interferon betas. While disease progression occurred in 16% of the women taking natalizumab, it was somewhat reduced in those for whom medication was reintroduced earlier, the study found.

“Our findings suggest that if women who take natalizumab for MS want to become pregnant, it may be best to continue treatment up until a pregnancy test is positive and then at that point discontinue use,” explained lead author Emilio Portaccio, MD, of the Don Carlo Gnocchi Foundation in Florence, Italy. “While there is still a risk of increased disease activity, this course of action may lower that risk.”

As for risks to the fetuses, the study group found that, for pregnancies exposed to natalizumab in the first trimester, the risk of miscarriage was four times higher than pregnancies where a mother took interferon betas or nothing for MS. The rate of 17% for natalizumab-exposed pregnancies was not much greater than the rate for the general population, which was 14%, the researchers point out.