Strength and Limitations of study
Our study is the first large cohort study that demonstrated gradual change in sleep quality along with blood pressure changes throughout pregnancy, via which the correlation between sleep and BP was better scrutinized. As sleep pattern may gradually change over time, sleep quality in the first visit may not be representative of the overall sleep pattern throughout pregnancy. The correlation between sleep and BP were individually assessed at each visit and that accounts for the most direct correlation if there is any. Follow up rate of our study is very high which makes the data more reliable.
Blood pressure varies throughout the day and is affected by activities immediately prior to blood pressure measurement. Our study only used a single point blood pressure during each visit for assessment. This may cause some inaccuracy and error as it may not be representative of the actual blood pressure. If possible, 24-hour ambulatory pressure would be a better modality for the accurate assessment of blood pressure, although it is logistically much more difficult to execute. Presence of sleep disorders such as sleep apnoea and subjects’ psychiatric history such as and history of depression were not explored in our study. These factors can potentially affect sleep quality and blood pressure and it would be ideal if these factors can be adjusted in the analysis.