Poor sleep associated with higher blood pressure in pregnancy: NORA Study

Uterine artery Doppler studies have long been employed to identify patients at risk of developing hypertensive disorders in pregnancy, especially pre-eclampsia. Resistance to blood flow in the uteroplacental circulation is reflected by increased uterine artery impedance, measured as pulsatility index (PI) and resistance index (RI). Uterine artery PI and RI values decrease with increasing gestational age as a result of trophoblastic invasion in a normal pregnancy. Derangement in trophoblastic differentiation hinders the physiological drop in uterine artery impedance during pregnancy and can potentially lead to hypertensive disorder and its associated complications, including fetal growth restriction and placenta abruption.

Tang Y and team carried this prospective study to delineate the association between sleep quality and BP throughout the entire pregnancy in individuals with no pre-existing hypertension. Uterine artery PI and RI were also assessed in relation to sleep quality.

The Neonatal and Obstetric Risk Assessment (NORA) study was a longitudinal prospective study conducted in KK Women's and Children's Hospital, Singapore, between 1 September 2010 and 31 August 2014. Participants were women with singleton pregnancies who attended antenatal clinics from their first trimester. Women with viable singleton pregnancies confirmed by ultrasonography at less than 14 weeks of amenorrhoea were considered eligible.

A total of 934 women (92%) completed all four antenatal follow-up visits and 926 women had complete delivery information. In the analysis, 10 women who had pre-existing hypertension were excluded, bringing the final number of subjects to 916. They were followed up throughout pregnancy with sleep quality, blood pressure and uterine artery Doppler assessed at each visit.

Sleep quality was assessed via the Pittsburgh Sleep Quality Index (PSQI) questionnaire during four visits: 9– 14 weeks of gestation (visit 1), 18–22 weeks of gestation (visit 2), 28–32 weeks of gestation (visit 3) and 34– 39 weeks of gestation (visit 4).

Four main questions were asked in the questionnaire:

(1) During the past month, what time have you usually gone to bed at night?

(2) During the past month, how long (in minutes) has it usually taken you to fall asleep each night?

(3) During the past month, what time have you usually got up in the morning?

(4) During the past month, how many hours of actual sleep did you get at night, which may be different from the number of hours you spent in bed?

PSQI score was calculated after combining the scores for each question. Women with poorer sleep quality have higher PSQI scores.

Sleep quality score, as represented by PSQI, increased from a median of 6 at the first visit to 7 at the last visit. Based on the mean value, the overall sleep quality and sleep efficiency worsened, sleep duration shortened and sleep latency increased as pregnancy progressed.

During the first visit, SBP, DBP and MAP were all significantly lower in women with longer duration of sleep. Likewise, SBP, DBP and MAP were significantly lower in women with a better sleep efficiency. No significant difference in BP was found in women with different sleep qualities during the second and fourth visits. DBP and MAP were significantly lower in subjects with better sleep efficiency during the third visit.

When overall sleep and BP were assessed throughout the entire pregnancy, a lower PSQI score (P < 0.001), shorter sleep latency (P = 0.008) and better sleep efficiency (P = 0.008) were found to be correlated with lower DBP. Longer sleep duration was associated with lower SBP (P = 0.049) and DBP (P = 0.008).

Assessment of the overall relationship between sleep and uterine artery Doppler throughout pregnancy showed that poorer sleep quality (higher PSQI, longer sleep latency, shorter sleep duration and worse sleep efficiency) were associated with higher uterine artery PI. Patients with higher PSQI and shorter sleep duration were also found to have higher uterine artery RI.

Study results showed that blood pressure (SBP and/or DBP and/or MAP) was lower in pregnant women with better sleep quality: shorter sleep latency, longer duration of sleep, better sleep efficiency and lower PSQI scores. Uterine artery PI was similarly lower in women with better sleep quality. The association between sleep and BP was the most significant in the first trimester as demonstrated by liner regression analysis.

The association between sleep disturbances and higher blood pressure demands that clinicians and researchers recognise the importance of sleep during pregnancy and explore ways to improve sleep antenatally. Most obstetric units do not routine screen for sleep disruption. A short questionnaire on sleep quality can be incorporated into routine obstetric care. Early identification of patients at risk of sleep disturbances and intervention at an early stage may benefit pregnancy outcome.

This cohort study shows an association between sleep and blood pressure throughout pregnancy in the population without a pre-existing hypertensive disorder. The most significant association was found in the first trimester. Uterine artery Doppler was worse in poorer sleepers, suggesting a potential association between sleep and placental function which may affect blood pressure. Future studies should focus on interventions to improve sleep antenatally in an effort to optimise blood pressure and pregnancy outcome.

Source: Tang Y, Zhang J, Dai F, Razali NS, Tagore S, Chern BSM, Tan KH. BJOG 2021;128:1192–1199

DOI: 10.1111/1471-0528.16591