Exposure to disease-modifying therapy during pregnancy: How worried should we be?

Many women, myself included, upon finding out that they are pregnant, experience about 90 seconds of pure joy before beginning to inventory every single thing that we ate, drank, inhaled or injected from the moment of conception. We all worry that we may have put something in our bodies that would somehow harm our babies.
Most of the disease-modifying therapies (Avonex, Betaseron, Rebif, Tysabri, Gilenya) fall into FDA pregnancy category C, with the exception of Copaxone, which is a category B medication.
Category C drugs carry the following warning: "Animal reproduction studies have shown an adverse effect on the fetus and there are no adequate and well-controlled studies in humans, but potential benefits may warrant use of the drug in pregnant women despite potential risks."
In other words, according to this categorization, it is probably not considered a good idea to use these drugs during pregnancy. Indeed none of the disease-modifying therapies are approved for use during pregnancy. Most neurologists have their patients with MS discontinue their disease-modifying therapies (DMTs) about a month before they begin trying to conceive. If a woman conceives while taking one of these medications, she is told to stop taking it immediately. All of these precautions are to protect the unborn baby.
However, there is a difference between mega-doses given to lab animals and what happens in real life when women take the drugs.
A couple of presentations at the ECTRIMS 2011 conference examine what actually happens to babies when there is brief exposure to these drugs prior to conception and during early pregnancy. The answer so far seems pretty clear: not much happens at all.
One group conducted a meta-analysis looking at 12 different studies where a total of 1105 pregnant women with MS were exposed to interferon therapy (Rebif, Avonex or Betaseron). In 10 of these studies, there was no evidence of an increase in miscarriage or birth defects in exposed pregnancies. In only one of the studies, there was a much higher rate of miscarriage in the group that was exposed (39%) than there was in the control group (5%) – for reference, the average miscarriage rate in the general population is between 15 and 20%. Another of the studies involving with what was considered an inadequate number of women found that 12.5% of pregnancies exposed to interferons prior to conception developed birth defects.
Another study from Latin America followed 43 pregnancies involving "long-term" exposure (defined as at least 8 weeks of continuous exposure) to Copaxone (24), interferons (16), IVIG (2) and Solu-Medrol (1). Again, there was no difference in miscarriage or birth defect rates between the exposed group and a control group of 78 women with MS who were not exposed to DMTs during pregnancy.
Data from the Tysabri Pregnancy Exposure Registry is also failing to show a correlation between exposure to Tysabri and adverse pregnancy outcomes. It should be noted, however, that "exposure" in this case is defined as getting a dose of Tysabri within the 90 days before becoming pregnant and not necessarily receiving Tysabri after conception.
Interestingly, all studies except the Tysabri data did show a slightly lower birth weight in babies who had been exposed to DMTs, but still within a normal range.
Bear in mind that these studies focused on the babies of women who used a therapy very early, before they even knew they were pregnant, and that the vast majority were taken off their meds when their pregnancy was discovered. So it’s hard to draw conclusions about what the outcomes might be if babies were exposed to these medications throughout the pregnancy. Since it’s unlikely that anyone will do a study that tests these risks full term, all we have to go on are these accidental exposures.
So, where does this information get us? At the very least, it seems to tell us that accidental exposure to your MS DMTs before you know you are pregnant should be nothing to worry about, so take that off your list of stressors.
I hope that this issue will be carefully considered and weighed in the future, so that docs and patients can be given clear direction based on real life evidence. Of course, all treatment decisions before, during and after pregnancy are to be made in conjunction with the doctor that is treating your MS and your OB/GYN.
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Julie Stachowiak, PhD

Julie is the author of the Multiple Sclerosis Manifesto, the winner of the 2009 ForeWord Book of the Year Award in the Health Category. She is an epidemiologist who is also a person living with MS, Julie has an in-depth understanding about current research and scientific developments around MS. She also has first-hand knowledge of the frustrations and anxiety surrounding the disease, as she had MS for at least 15 years before receiving a diagnosis in 2003 and has had several relapses since her diagnosis.