Pregnant women with multiple sclerosis (MS) exposed to Tysabri (natalizumab) in the first trimester had higher rates of miscarriage and major birth defects in their babies, than women left untreated or treated with interferon beta, a study shows. Although higher, these rates were similar to those in the general population.
Longer periods without treatment before pregnancy, and resuming treatment only a month or more after giving birth, also were found to be associated with increased risk of relapse in mothers with MS.
The results used data from multiple centers across Italy and were published in two articles in the journal Neurology.
During clinical trials testing disease-modifying therapies for MS, such as Tysabri (marketed by Biogen), women typically had to undergo contraception measures and had to leave the trial if they became pregnant. As a result, how this type of medication affects pregnancy outcomes remains unknown, creating a significant knowledge gap when considering that MS affects mainly women during their reproductive years.
A group of researchers collected data from 19 centers across Italy for all the pregnancies that occurred between 2009 and 2015 in women with MS treated with Tysabri.
They compared pregnancy outcomes, focusing specifically on miscarriages and major congenital anomalies (birth defects), with those of untreated women and women treated with interferon beta medications. Researchers also compared the results with that of the general Italian population.
The study reporting the findings is titled “Pregnancy decision-making in women with multiple sclerosis treated with natalizumab I: Fetal risks.”
The team identified 92 pregnancies in 83 women taking Tysabri for relapsing-remitting MS. Researchers followed up with these women every six months, when they had a relapse, and again one year after they gave birth.
The analysis showed that exposure to Tysabri during the first three months of pregnancy was associated with a 17.4 percent risk of miscarriage, which is higher than that of untreated or interferon beta-treated women. The risk of major birth defects in the Tysabri group was 3.7 percent, a value also higher than that of the control group (untreated and interferon-beta).
However, despite the higher risk for miscarriage and major birth defects associated with Tysabri, these are within the estimates for the general population.
Both Tysabri and interferon-beta treatments were associated with lower length and weight of babies.
In a second study, “Pregnancy decision-making in women with multiple sclerosis treated with natalizumab II: Maternal risks,” researchers reported the risk for disease relapse.
Women exposed to Tysabri during the first trimester increased their relapse rate (during and after pregnancy) by three times compared to the control groups.
A longer period with no treatment (“washout period”) before pregnancy resulted in a higher risk of relapse during pregnancy. Disease progression affected 13 percent of the women in the control group and 16 percent in the Tysabri-treated group, but was reduced in women who resumed Tysabri within one month after childbirth.
These results suggest that avoiding long washout periods and early reintroduction of disease-modifying therapy after delivery may decrease the risk of relapse.
“This study adds important information about how medications may affect women with MS who are exposed to treatment during pregnancy, and their babies,” Kathleen Costello, associate vice president of Healthcare Access for the National MS Society, said in a press release.
“But the decision about taking disease-modifying therapies during pregnancy should not be based on one study. Many factors need to be considered as women and their healthcare providers weigh the risks and benefits of treatment and determine the best path forward,” Costello said.
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