My MS story
Why Women With MS Feel Better During Pregnancy
Past research has focused on hormones, but some researchers are exploring other possibilities for pregnancy’s effects on MS.
By Cathy Cassata
Medically Reviewed by Samuel Mackenzie, MD, PhD
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It’s a known phenomenon that most women with multiple sclerosis (MS) feel better and experience fewer relapses while pregnant. This is especially the case during the second and third trimesters, according to the National Multiple Sclerosis Society (NMSS). Relapse rates then tend to rise in the first three to six months postpartum (after giving birth): A woman has a 20 to 40 percent chance of having a relapse during this time, says the NMSS.
For years, researchers have speculated that changing levels of hormones, such as estrogen and progesterone, are linked to these trends. But studies on the effects of hormones on MS have had mixed results, and some experts now believe that hormones aren’t involved at all.
“The clinical trials that have been done in relation to hormones have not been as impressive as we had hoped,” says James D. Bowen, MD, medical director of the Multiple Sclerosis Center at the Swedish Neuroscience Institute in Seattle. “This has changed my thinking on the whole issue of why women do better during pregnancy.”
Nothing to Do With Hormones
Dr. Bowen is currently taking part in preliminary research that looks at something called microchimerism, the presence of a small number of cells in one person that originated in another person — in this case, the presence of fetal cells in the mother.
Bowen has teamed up with J. Lee Nelson, MD, an autoimmunity researcher and rheumatologist at the Fred Hutchinson Cancer Research Center and professor of medicine in the division of rheumatology at the University of Washington, both in Seattle. Dr. Nelson is one of the world’s leading researchers on mother-child cell transfer and how it relates to rheumatoid arthritis (RA). She has conducted years of research looking into how cells travel between mother and fetus through the placenta, and what this means for women with RA.
Nelson noted that during pregnancy, a woman is capable of carrying a child that holds half of the father’s genes. But in other circumstances, if she were to receive something that was genetically half foreign — such as an organ from a parent, child, or sibling — her body would reject it.
“There’s no degree of estrogen or immune suppressant drugs that you could give a kidney transplant patient that would make them tolerate a mismatched kidney, so why does a mother tolerate a horribly mismatched baby for nine months?” asks Bowen. “We don’t think hormones could possibly be the answer,” he says.
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“One reason is that hormones don’t suppress the immune system to that degree. Also, the way sex hormones act is that they serve as transcription factors: They get into the cells and change the genes that are encoded and change what proteins that cell is making, so they affect every cell. If hormones were affecting lymphocytes [white blood cells responsible for immune responses], it would affect all lymphocytes. So how does the mother turn down the immune system against the fetal antigens without getting severely immune suppressed and dying of infectious diseases?”
Nelson’s RA research may have the answer: She discovered that if a baby had a different genetic makeup from the mother, the mother had an immune response that led to improved RA symptoms during pregnancy. Nelson also found that the amount of fetal material found in the mother’s blood correlated with whether or not she went into remission.
For instance, women who had high levels of the foreign cells in their blood went into full remission during pregnancy, and when RA symptoms returned, those foreign cells were no longer detected. And the women who didn’t improve during pregnancy showed few fetal cells in their blood.
Breaking Ground for MS
Since MS, like RA, is an autoimmune disease in which women often do better during pregnancy and worse after delivery, Nelson and Bowen are conducting similar research on pregnant women who have MS.
They are currently gathering pilot data on eight pregnant women with MS. Through blood samples taken before, during, and after pregnancy, Nelson and Bowen are measuring the women’s fetal cells as a demonstration study to show that they can, in fact, identify fetal cells in the mother’s bloodstream.
“We hope to use this data to get a grant for a larger study that would look into whether or not a baby’s T Cells are indeed the reason behind why women with MS feel better during pregnancy,” Bowen says.
Bowen and Nelson’s thinking revolves around the idea that babies leak more and more cells into their mother’s bloodstream as they develop, and by the time the third trimester comes along, about 6 percent of the DNA in the mother’s blood is fetal. Bowen explains that most of these cells are regulatory T Cells, which are capable of turning down the mother’s immune system in a very specific way that prevents it from attacking the baby’s brain.
“In turn, if the mother has MS, her brain would benefit from that very specific immune suppression [that] leaves the rest of her immune system intact to fight off things like pneumonia and other illnesses,” Bowen says.
What Happens After Birth
When the umbilical cord is cut, Bowen says, so is the supply of fetal cells — which is why women with autoimmune diseases relapse. But a small number of fetal cells take up permanent residence in the mother’s bone marrow, he notes.
“The more of these cells a woman has permanently, the better her RA does in the long run,” says Bowen. “We don’t have data on this in regards to MS, but there was a study in Australia that showed the more babies a woman had, the better her MS did. Our thinking behind that is with each pregnancy, the mother gets a small dose of microchimerism.”
Bowen says a more in-depth study on MS and microchimerism could lead to future treatments for the disease.
“Right now, pregnancy is one of our most powerful treatments,” Bowen says. “It decreases attacks by two-thirds. Not too many of our drugs do that.
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