Chronic hypertension affects approximately 2 % of all pregnancies and is associated with adverse maternal and perinatal outcomes including preeclampsia/eclampsia, stroke, intrauterine growth restriction, preterm birth and perinatal death. [1], [2], [3], [4] Preeclampsia, a hypertensive complication superimposed on chronic hypertension in pregnancy, occurs in up to one-third of patients with chronic hypertension and is a significant driver of adverse outcomes. [5], [6], [7], [8], [9], [10] However, the differentiation between chronic hypertension and superimposed preeclampsia poses a diagnostic dilemma that is especially challenging in patients with previously undiagnosed chronic hypertension. Due to physiologic decreases in systemic vascular resistance in pregnancy, blood pressure decreases in the first and second trimesters, with a 10 % decrease as early as the 7th week of gestation. This can mask previously undiagnosed chronic hypertension and is especially problematic in patients who initiate prenatal care after the first trimester. As blood pressure returns to pre-pregnancy levels in the third trimester, it is possible to misdiagnose a return to undiagnosed pre-pregnancy chronic hypertension as gestational hypertension. Further, a minority of patients with chronic hypertension have baseline proteinuria due to renal complications of hypertension, obfuscating the distinction between preeclampsia and undiagnosed chronic hypertension. Although superimposed preeclampsia may be suspected in patients with chronic hypertension in the setting of increased proteinuria or blood pressures above baseline, it remains a diagnosis of exclusion [4], [6], [11], [12].

Given these diagnostic dilemmas, we aim to assess contemporary patterns of physiologic blood pressure changes throughout pregnancy in patients with hypertension who do and do not develop preeclampsia, as compared to patients with no history of hypertension with normal pregnancy outcomes, hypothesizing that blood pressure trajectories among these groups of pregnant patients are different.