Statistical analysis
Statistical analysis of the data was performed using SPSS 22.0 (IBM,
Armonk, NY, USA). For maternal demographic and lifestyle
characteristics, continuous variables were described as mean ± standard
deviation. Categorical variables were described as the sample number and
frequency of each category. Step wise linear regression was performed
across the four visits on the following variables: PSQI, sleep latency,
sleep duration and sleep efficiency to establish the relationship
between sleep quality and blood pressure throughout pregnancy, after
considering potential confounding factors. Data from each individual
visit was analysed separately. Mixed model analysis was employed to
study the overall correlation between sleep and BP as well as
sleep and uterine artery resistance and pulsatility index, combining the
information from all 4 antenatal visits. Analysis was adjusted for
possible confounders.