Pregnancy is a risk factor for restless legs syndrome

Pregnant women are at higher risk for the occurrence or worsening of restless legs syndrome (RLS), a movement disorder that affects up to 10 percent of the general population, according to a study reported in the September 28 issue of Neurology, the scientific journal of the American Academy of Neurology.

Researchers in Milan, Italy, recently concluded a large and detailed epidemiological study on RLS during pregnancy and six months postpartum that demonstrates at least one in four pregnant women experience RLS. RLS is characterized by an urge to move the legs, generally accompanied by unpleasant numbness, tingling, or burning sensations; an increase in symptoms during rest and a partial, temporary relief from symptoms through activity; and a worsening of symptoms in the evening or at night. Symptoms tend to progress with age.

The association between RLS and pregnancy was noted first in 1940, and confirmed later by a few epidemiological investigations. “While several attempts have been made to study the connection between pregnancy and RLS, ours is the first epidemiological study to use the four standard International RLS committee diagnostic criteria,” noted Mauro Manconi, MD, of the Sleep Disorders Center at Vita-Salute University, Milan.

A total of 606 women, admitted to the Department of Gynecology and Obstetrics of Ferrara University between February and June 2002, were included in the study. Two neurologists certified in sleep medicine interviewed the women within two days of delivery, and those affected by RLS were interviewed again at the end of the first, third, and sixth month after delivery. The initial interview included demographic data, personal and family medical history, course of pregnancy, physical measurements of mother and newborn, iron and folate therapy, sleep habits, and presence of sleep disorders. A detailed description of RLS symptoms, if present during and before pregnancy, was also evaluated. A woman was considered affected by RLS if she met all four International RLS Study Group criteria.

Of the 606 women in the study, 161 (26.6 percent) reported the occurrence of RLS, 101 of whom reported experiencing RLS for the first time. One-fourth of the women experienced RLS symptoms at least once a week, and 15 percent at least three times a week. The appearance or worsening of RLS symptoms was generally around the sixth month, reaching a peak at the seventh and eighth months of pregnancy. RLS prevalence dramatically decreased around the time of delivery, ranging between five and six percent at six months postpartum.

RLS symptoms had a significant impact on sleep, with affected women reporting a reduced total sleep time, longer sleep latency, and more frequent insomnia and excessive daytime sleepiness compared to non-affected women. “The pregnant women most affected by RLS were older, had lower values of iron storage indicators, a higher prevalence of insomnia, and snored more than the unaffected group,” commented Manconi. However he also said, “Our results on a significant difference in iron storage indicators support a hypothesis that a relative iron deficit could play a role in this form of RLS, though the rapid improvement of RLS symptoms after delivery give more power to a hormonal rather than iron-related hypothesis.”

Even if the real cause of the association between RLS and pregnancy remains unclear, this study is the first to show a significant correlation between low iron indicators values and the risk to develop RLS. Further investigations are needed to evaluate the role of hormonal state and of personal genetic background predisposition in the cause of this temporary state of RLS.