Periodic limb movements in sleep during pregnancy: a common but benign disorder?

Pregnant women have a two- to threefold increased prevalence of restless legs syndrome (RLS) compared to the general population, and the majority of RLS patients also experience periodic limb movements in sleep (PLMS). PLMS have been associated with sleep disturbance as well as autonomic heart rate and blood pressure responses; however, the prevalence, cause and significance of PLMS during pregnancy remain unknown. This study evaluated the presence of PLMS in late pregnancy and its relationship to hypertensive disorders of pregnancy. Ninety-one women in the third trimester of pregnancy underwent overnight polysomnography. An RLS questionnaire and the Multivariate Apnea Risk Index were administered and venous blood was sampled within 2 weeks of the sleep study. After exclusions due to obstructive sleep apnoea and signal loss, PLMS data were available for 73 women, 36 hypertensive women and 37 BMI- and gestation-matched controls. PLMS were found to be very common during pregnancy; 45% of women had a PLMS index > 5 and 25% had a PLMS index > 15. The number of PLMS per hour did not differ by hypertensive status. Sleep quality was mostly unaffected by PLMS, as was change in blood pressure overnight. While RLS was reported by 18.3% of the sample, this did not reliably predict the presence of PLMS. Despite iron deficiency being common in this population, it was not associated with PLMS. This novel study investigating the frequency and impact of PLMS during pregnancy revealed that PLMS are very common in the third trimester; however, this disorder appears to be benign in terms of objective sleep quality and relationship with pregnancy-related hypertension.