Capillary remodelling in normal pregnancy: Can it mediate the progressive but reversible rise in blood pressure? Novel insights into cardiovascular adaptation in pregnancy

Objective: To conduct a longitudinal study of skin capillary density changes throughout normal pregnancy and correlate them to changes in blood pressure.

Design: Prospective, longitudinal cohort study.

Setting: London teaching hospital.

Study design: Two hundred and twenty-five Caucasian, Primigravid women with singleton pregnancy, normotensive throughout pregnancy, and with normal pregnancy outcomes. We used intra-vital video microscopy to measure basal (i.e. functional) and maximal (i.e. structural) skin capillary density (CD) according to a well-validated protocol. The subjects were studied at baseline (11-16weeks gestation) and at four consecutive visits (20-24weeks, 27-32weeks, 34-38weeks, and 5-15weeks postpartum). Blood pressure measurements were taken during the same visits.

Results: We found that normal pregnancy was associated with progressive capillary rarefaction, with the overall trend in the fall in both functional and structural CD being statistically significant (p<0.001). The fall in CD was a remarkable mirror image to a progressive rise in systolic and diastolic blood pressures, there being a significant correlation between systolic blood pressure and structural CD. Postpartum measurements of both CD and blood pressure were similar to base line levels.

Conclusions: Progressive capillary rarefaction is a normal accompaniment of human pregnancy that may mediate the progressive rise in systolic and diastolic pressures. Both the CD and blood pressure changes are reversible, returning to baseline in the puerperium.