Prior Pregnancy, But Not the Pill, May Protect Against MS

The risk of developing multiple sclerosis (MS) is lower in women with a history of pregnancy and is not affected by the use of oral contraceptives, according to a recent meta-analysis of four published studies.

However, the four studies, conducted in the U.S. and Iran, showed considerable variability in their findings, particularly regarding the use of oral contraceptives, known colloquially as “the pill.”

The analysis, “Pregnancy History, Oral Contraceptive Pills Consumption (OCPs), and Risk of Multiple Sclerosis: A Systematic Review and Meta-Analysis,” was published in the International Journal of Preventive Medicine. 

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A combination of factors, including genetic and environmental, are thought to contribute to MS development. Women are predominately affected by the disease, which has raised the hypothesis that sex hormones could be involved in its development and progression.

Various factors that can influence hormone levels, such as age at menstruation onset, history of pregnancy, number of pregnancies, and use of oral contraceptives, have been shown to influence MS risk in women.

Several studies have shown a history of pregnancy confers protection against MS development, although the magnitude of that effect varies significantly across studies. In contrast, other research has shown that prior pregnancy or breastfeeding had no effect on MS risk.

Likewise, the relationship between oral contraceptive use and MS risk remains controversial. While some studies show an increased risk of MS development or a more aggressive disease course with the use of these medications, others show a protective effect or no relationship at all.

Therefore, researchers in Iran set out to clarify these relationships by conducting a review and meta-analysis of four previously published studies on contraceptive use or pregnancy history and MS risk.

The analysis included four case-controlled studies, meaning they included women who developed MS and those who did not. Two studies were conducted in the U.S. and two in Iran.

In the three studies that analyzed pregnancy history, results generally showed a decreased risk of MS with at least one prior pregnancy. Overall, the odds of developing MS were reduced by 36% in women with a pregnancy history compared with those who had never been pregnant.

The researchers suggested that the protective effects of pregnancy could be related to a modulation of the immune system by sex hormones.

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Across all four studies, findings about oral contraceptive use and MS risk varied. In the meta-analysis, oral contraceptives were not found to significantly influence MS risk. Further analyses indicated that the observed variability was not associated with the country in which the study was conducted.

“The results of this systematic review show that pregnancy history is a protective factor for MS development, whereas [oral contraceptive] use has no significant effect,” the researchers wrote.

They noted, however, that study findings were limited by the few studies included in the analyses, as well as by the high level of variability between them.