Epidemiology

A possible relation between restless legs syndrome (RLS) and pregnancy was noted by Mussio-Fournier and Rawak in 1940.¹ They reported the occurrence of a symptoms characterized by “pruritus, urticaria and paresthesias” of the lower limbs, appearing during rest, in three subjects belonging to the same family. The authors focused on one member of the family, who presented with a typical worsening of the symptoms during pregnancy. In 1945, Ekbom² performed the first structured epidemiologic study on this topic, finding a prevalence of RLS of 11.3% among 486 pregnant women. A few years later, Jolivet,³ in his degree thesis in medicine, reviewed a population of 100 pregnant women and observed 27 cases of RLS. The same topic was further investigated by only a few other epidemiologic studies (Table 23-1), which found an RLS prevalence during pregnancy ranging from 11% to 27%.^2–7 The high variability of these rates could be related to several differences in methodology between the studies. Standardized formal criteria^8,9 for making the diagnosis of the RLS were used in only one of these studies. The diagnosis was assessed either by self-administered questionnaire or by face-to-face medical interview. The minimal frequency of RLS symptoms required to define “affected” women varied between studies or was not even stated in the methods. The studies have been performed in different geographic areas and on different racial populations. Finally, the time during the pregnancy at which the presence or absence of symptoms was evaluated also varied between studies. Because the prevalence of RLS appears to increase for the duration of the pregnancy,¹⁰ this sampling method would clearly bias the prevalence rates that were reported. When the prevalence rate is ascertained by applying the standard diagnostic criteria through a structured medical interview, on a wide and homogeneous population of women, and during the entire course of pregnancy, the frequency is about 26%.⁷ Another study found that, even excluding those with preexisting RLS, the prevalence of RLS was 26% when examined in late pregnancy.^7a This prevalence rate is much higher than that reported for the general population and includes women who had RLS before the pregnancy, as well as those who developed RLS during pregnancy. The percentage of women with preexisting RLS ranges between 5% and 10%. In most cases, however, these women reported a significant worsening of the symptoms during the pregnancy.⁷

The higher prevalence of RLS during pregnancy and the close temporal relationship between the symptoms occurrence and the pregnancy time have led to the suggestion that, under these conditions, RLS should be considered a secondary or symptomatic form. However, the term “symptomatic” seems not completely appropriate, because pregnancy is a physiologic and not a pathologic condition, whereas the term “secondary” suggests a precise causal relationship between two variables that in the specific case is not so well delineated. Therefore, when considering RLS in relation to pregnancy, it would be more correct to consider pregnancy as a strong risk factor for RLS, as, for example, obesity is for sleep apnea.

Course and Prognosis

The RLS prevalence is not uniform during pregnancy; it increases progressively starting from the third and four months of gestation and reaches a peak during the third trimester, especially in the eighth month, in which the highest rate is observed. After that it rapidly declines during the ninth month, to disappear around the time of delivery. During the puerperium, the prevalence is about that found during the prepregnancy period^5,7 (Fig. 23-1). In women not previously affected by RLS, the mean duration of symptoms during pregnancy usually is 3 to 5 months. Unfortunately, longitudinal data do not yet exist regarding the risk of developing RLS in the future for those who had symptoms only during pregnancy.

FIGURE 23-1. Prevalence course of restless legs syndrome (RLS) throughout pregnancy and puerperium. RLS (thick line), total RLS group; *RLS (dotted line), women affected by RLS only during pregnancy; pRLS (dashed line), preexisting RLS group; Arabic numerals, month during pregnancy; Roman numerals, months postpartum.

The intensity and the frequency of occurrence of the symptoms seem to follow the same trend of the prevalence, characterized by a significant worsening in the third trimester, both in the women already affected by the disease before pregnancy and in women with symptoms for the first time.

Multiparous women often reported having RLS symptoms during the previous pregnancies.^5,7 The quality of RLS symptoms, including its anatomic distribution, circadian nature, and relief with motor activity, are not different during pregnancy than those reported by those with idiopathic RLS.⁷ Familiar RLS history is a common finding, especially for women affected by a preexisting form of RLS.

Sleep Impact

The consequences of the symptoms on the pregnant women sleep are usually not dramatic. Some women with RLS report higher sleep latency, excessive daytime sleepiness, lower total sleep time, and, more frequently insomnia, compared with unaffected pregnant subjects.⁷ In a few cases the symptoms became very disagreeable, making it impossible for those so affected to relax in the evening or to fall asleep.¹¹ Pregnancy itself, particularly during the third trimester, is frequently associated with sleep loss often secondary to many factors (nocturia, fetal movements, gastroesophageal reflux, snoring, sleep apnea, forced body position, and anxiety about the delivery).¹²