Physiology of blood pressure relevant to managing hypertension in pregnancy

PURPOSE: Pregnancy causes physiological changes in maternal organ systems, and blood pressure (BP) is one of the variables affected. This review is focusing on the physiology of BP relevant to the management of hypertension in pregnancy. MATERIALS AND METHODS: A detailed literature search was performed using electronic databases (including WorldCat, PubMed, MEDLINE, Google Scholar) to retrieve and review reports related to physiology of BP in pregnancy. RESULTS: During pregnancy, there is vasodilation caused by mediators such as increased levels of progesterone and nitric oxide. The vasodilation leads to a reduction in vascular resistance, BP, and renal blood flow. In compensation, the following postulated events occur: activation of renin-angiotensin-aldosterone axis, resetting of osmotic threshold for thirst, and an increase in the production of vasopressin. Sodium and water conservation ensue to increase the total body water, end-diastolic volume, cardiac output, and BP. The increase in cardiac output incompletely compensates for the decreased vascular resistance, and BP therefore decreases in midpregnancy and returns to prepregnancy level toward term. CONCLUSIONS: An understanding of the physiological changes in BP is essential for appropriate management of pregnancy-related hypertension.