Objective: To elucidate the correlation between sleep disturbances and blood pressure during pregnancy in women with no pre-existing hypertension. Design: Prospective cohort study. Setting: Outpatient specialist clinics at KK Women’s and Children’s Hospital, Singapore. Population: Women with viable singleton pregnancies confirmed by ultrasonography at less than 14 weeks of amenorrhea at first visit. Methods: 926 subjects were recruited for this study in the outpatient specialist clinics at KK Women’s and Children’s Hospital, Singapore, between September 1, 2010, and August 31, 2014. They were followed up throughout pregnancy with sleep quality, blood pressure and uterine artery doppler assessed at each visit. Main outcome measures: sleep quality, blood pressure and uterine artery doppler. Results: Sleep progressively worsened as pregnancy advances. Shorter sleep duration and poorer sleep efficiency were associated with higher blood pressure, especially in the first trimester. Mixed model analysis demonstrated overall positive correlation between sleep quality represented by Pittsburgh Sleep Quality Index (PSQI) score and diastolic blood pressure (DBP) (p<0.001) and mean arterial pressure (MAP) (p=0.005) during pregnancy after considering all trimesters. Sleep duration was found to be negatively correlated with both systolic blood pressure (SBP) (p=0.029) and DBP (p=0.002) while sleep efficiency is negatively correlated with DBP (p=0.002) only. Overall poor sleep during pregnancy was also found to be correlated to higher uterine artery pulsatility index. Conclusion: Our prospective study demonstrated that sleep quality is significantly correlated with blood pressure during pregnancy with most prominent effect in the first trimester.