Are blood pressure level and variability related to pregnancy outcome? Analysis of control of hypertension in pregnancy study data

Objective: To examine the relationship between pregnancy outcomes and BP level and variability.

Design: Secondary analysis of CHIPS trial data (Control of Hypertension In Pregnancy Study, NCT01192412).

Setting: International.

Population or sample: Women with chronic or gestational hypertension.

Methods: BP measurement was standardised in outpatient clinics. Adjusted (including for allocated group) mixed effects logistic regression was used to assess relationships between major CHIPS outcomes and both BP level (mean of clinic readings) and visit-to-visit within-participant BP variability (standard deviation and average real variability of absolute successive difference of BP values). BP values 7-28 days prior to outcomes (or birth for perinatal outcomes) were excluded in sensitivity analyses.

Main outcome measures: Major CHIPS outcomes.

Results: Among 961 (97.4%) women, higher BP level was associated with more adverse maternal and perinatal outcomes (usually at p < 0.001) except for serious maternal complications. Among 913 (92.5%) women with at least two post-randomisation outpatient visits, higher BP variability was associated with increased odds of severe hypertension and pre-eclampsia (usually at p < 0.01). Sensitivity analyses suggested reverse causality for these maternal outcomes, but greater diastolic BP variability may have been associated with fewer adverse perinatal outcomes.

Conclusions: Higher BP is an adverse prognostic marker, regardless of target BP. While the association between higher BP variability and severe hypertension and pre-eclampsia may be related to higher BP at diagnosis, our results suggest a possible advantage of BP variability for the fetus, through undefined mechanisms.

Tweetable abstract: Higher blood pressure (BP) is associated with more adverse pregnancy outcomes, but higher BP variability may be good for the baby.