Women between the ages of 18 to 40, during their childbearing years, are less likely than men to receive drugs for multiple sclerosis. Even when those drugs have been shown to be safe for use during pregnancy, or to have a prolonged effect against the disease even when stopped before conception, according to a new study.

For this study, researchers at the University of Lyon, in France, looked at more than 27 years of health records for people in France with relapsing-remitting MS that started when they were between 18 and 40 years old. A total of 16,857 women and 5,800 men were included in the study, with an average age of 29, and they were followed for an average of 12 years.

When researchers examined the percentage of person-years that people in the study received a disease-modifying drug, the number was 60.2 percent for women and 61.3 percent for men. Person-years represent both the number of people in the study and the amount of time each person spends in the study. For the highly effective drugs, the numbers were 23.5 percent for women and 25.3 percent for men.

However, researchers said these raw percentages do not take into account differences that might explain a gap in drug exposure between men and women such as disease severity since women tend to have a more active disease, or pregnancy and postpartum periods during which certain therapies may be interrupted.

After adjusting for disease severity, pregnancy, and postpartum periods, women had 8 percent lower odds of receiving a DMT compared to men. In the case of newer drugs that are highly effective at reducing MS relapses, women had 20 percent lower odds of receiving the drugs.

A limitation of the study was that information on pregnancies ending in miscarriage or stillbirth as well as unsuccessful attempts at pregnancy was not available. Therefore, discontinuations of medications because of these events were accounted for by adjusting the results for sex.

The study was published in the journal Neurology.