Patient characteristics decrease impact of race on restless leg syndrome in pregnancy

Incident restless leg syndrome during pregnancy was common and varied by race and ethnicity, a finding that was likely accounted for by differences in age, parity and other risk factors, according to results from a multicenter study.

The researchers, who published their findings in Neurology, noted that the rate of restless leg syndrome (RLS) is about 20%, which is “much higher” than the rate of 2% to 10% in the general population. Previous research demonstrated extensive regional differences in the rates of RLS in pregnancy, according to the study findings.

“Racial/ethnic differences have been proposed to explain the difference due to genetic susceptibility and other environmental factors,” Muzi Na, PhD, MHS, assistant professor and Broadhurst Career Development Professor for the Study of Health Promotion and Disease Prevention in the department of nutritional sciences at Pennsylvania State University, and colleagues wrote. “However, few studies have examined RLS risk by race/ethnicity within the same population; in the US, most studies have been conducted in predominantly white samples.”

Na and colleagues analyzed data from the Fetal Growth Studies – Singletons trial, which was conducted by the Eunice Kennedy Shriver National Institute of Child Health and Human Development. The multicenter, multiracial prospective cohort study gathered data on 2,704 pregnant women (non-Hispanic white, n = 709; non-Hispanic Black, n = 765; Hispanic, n = 774; Asian or Pacific Islander, n = 456). Na and colleagues evaluated the incidence of restless leg syndrome (RLS) throughout pregnancy as well as risk factors, such as age and parity.

The findings demonstrated an overall new-onset RLS incidence of 18.1% at any point during pregnancy. This included incidence rates of 20.3% for white participants, 15.4% for Black participants, 17.1% for Hispanic participants and 21.1% for Asian or Pacific Islander participants (P = .03).

Analyses adjusted for age, parity, prepregnancy BMI, education, baseline iron-deficiency anemia and infant sex showed that these factors mitigated the difference in RLS risk across race/ethnicity groups. As a result, the relationship between race and RLS became insignificant in the overall sample (compared with white women: adjusted RR of RLS, 0.91 [95% CI, 0.71-1.16] for Black women; 1.05 [95% CI, 0.83-1.34] for Hispanic women; and 1.03 [95% CI, 0.82-1.31] for Asian women).

Among Hispanic participants, risk for RLS increased with older age (reference, 25 years; 25 to 35 years: RR = 1.51 [95% CI, 1.05-2.16]; 35 years or older: RR = 1.58 [95% CI, 0.93-2.68]) as well as in participants with iron deficiency anemia (RR = 2.47 [95% CI, 1.31-4.64]) and those with total greater skinfold at subscapular and triceps sites regardless of BMI (RR = 2.54 [95% CI, 1.30-4.97]). Conversely, multiparity correlated with lower risk among Hispanic participants (RR = 0.69; 95% CI, 0.50-0.96).

Na and colleagues found that greater skinfolds and waist circumference correlated with increased risk for RLS during pregnancy among Black participants, “though the trends were less clear.” They wrote that the findings from the present study “identified subcutaneous fatness as a potential novel risk factor of new onset of RLS in pregnancy independent from overall adiposity” and noted that the results also supported the potential impact of adiposity on RLS in pregnant women.

“Importantly, being specific about new onset of RLS in pregnancy, our study found that the risk of RLS by race was no longer significant, but remained similar in magnitude, after adjusting for several demographic, socioeconomic, and maternal pregnancy factors,” they wrote. “Future studies to understand the pathophysiologic mechanisms underlying the findings are warranted.”