Researchers say new, aggressive disease modifying therapies could be causing an increase in MS relapses after pregnancy.

Pregnancy is not bringing relief from multiple sclerosis as previously thought.

For years, patients with multiple sclerosis (MS) were told pregnancy could help prevent relapses. This was the conclusion after a 1998 study, and widely accepted ever since.

However, according to a new study, this is no longer the case.

And the cause may be the use of more aggressive disease modifying therapies (DMTs).

The Kuwait study concludes that using aggressive therapies, even with long “washout periods” before conception, was associated with a higher frequency of relapses during pregnancy.

Postpartum relapse occurrences were similar to those previously reported.

The 1998 study showed a significant drop in relapses during pregnancies, especially during the third trimester.

“These [1998] results inspired a lot of research,” Bruce Bebo, PhD, executive vice president of research at the National Multiple Sclerosis Society, told Healthline.

Bebo explained why these drops in relapses happen.

“Immune mechanisms are triggered during pregnancy to keep the mother from rejecting the fetus. They are also likely responsible for suppressing the immune system that triggers for relapses,” he said.

“There were some limitations to the [Kuwait] study,” Bebo noted. “The sample was taken from a registry and consisted of an homogenous population. It was a relatively small study with 87 patients. Additional studies with larger, more heterogenous populations will be needed to confirm this observation.”

Most likely, the “higher rate of relapses was driven by a rebound caused by a drug withdrawal,” said Bebo.

Many of the aggressive therapies are known to trigger MS exacerbations upon withdrawal.

The DMTs in the study included natalizumab (Tysabri) and fingolimod (Gilenya).

Bebo further explained how these drugs work on a basic level.

One sequesters inflammatory immune cells into the lymphatic cell system to keep MS at bay. Then, when the block is removed, they all escape and get into the nervous system, causing a relapse.

The other type of drug blocks immune cell entry into the nervous system. When the therapy stops, the dam breaks and these cells can get into the nervous system.

Often people experience a rebound or exacerbation when taken off these medicines.

“Patients are placed on these when they typically have failed to respond to one or more other treatments. These aggressive medicines come with side effects and risks,” Bebo explained.

Treating a progressive disease has risks.

“Relapses could be manifested by the rebound,” agreed Dr. Barbara Giesser, professor of clinical neurology at the David Geffen School of Medicine at the University of California, Los Angeles (UCLA) and clinical director of the UCLA MS program. “This would not explain the relapses in patients not on these agents, but might account for the higher incidence seen in those two groups.”

“There may be alternative explanations for the increase in relapse rate,” she added.

Giesser pointed out that the relapse rate was highest in patients who had been receiving natalizumab (Tysabri) and fingolimod (Gilenya) before pregnancy.

Both of these are DMTs that would more commonly be used in patients with a more active or aggressive form of the disease.

“That degree of disease activity may have accounted for the increased relapse rate,” added Giesser.

The study raises questions.

Bebo hopes it will inspire additional studies.

“Much of this data is already collected and out there in registries around the world.” Further studies would allow scientists to “better understand the relationship,” he said.

Bebo emphasized, “It is time to think about the effect of pregnancy in an era with potent DMTs.”

There are strategies for preparing oneself for conceiving. There are ways to prevent the rebound, before the relapse.

Bebo suggests working with a neurologist to design a treatment approach while considering conceiving a child, to create a plan that mitigates the risks.

Editor’s note: Caroline Craven is a patient expert living with MS. Her award-winning blog is, and she can be found on Twitter.