Objective: To estimate the prevalence and patterns of sleep disturbances during pregnancy among healthy nulliparous women. Methods: This was a prospective, cohort study of healthy nulliparous women, recruited between 6 and 20 weeks of gestation, who completed a baseline sleep survey at enrollment with follow-up in the third trimester. The survey was composed of the following validated sleep questionnaires: Berlin Questionnaire for Sleep Disordered Breathing, Epworth Sleepiness Scale, National Institutes of Health/International Restless Legs Syndrome Question Set, Women's Health Initiative Insomnia Rating Scale, and the Pittsburgh Sleep Quality Index. Differences in sleep characteristics between the baseline and third trimester were compared using the paired t test or McNemar test for continuous or categorical data, respectively. Results: One hundred eighty-nine women completed both baseline and follow-up sleep surveys. The mean gestational age was 13.8 (±3.8) and 30.0 (±2.2) weeks at the first and second surveys, respectively. Compared with the baseline assessment, mean sleep duration was significantly shorter (7.4 [±1.2] hours compared with 7.0 [±1.3] hours, P<.001), and the proportion of patients who reported frequent snoring (at least three nights per week) was significantly greater (11% compared with 16.4%, P=.03) in the third trimester. The percentage of patients who met diagnostic criteria for restless leg syndrome increased from 17.5% at recruitment to 31.2% in the third trimester (P=.001). Overall poor sleep quality, as defined by a Pittsburgh Sleep Quality Index score greater than 5, became significantly more common as pregnancy progressed (39.0% compared with 53.5%, P=.001). CONCLUSION: Sleep disturbances are prevalent among healthy nulliparous women and increase significantly during pregnancy.