The American College of Obstetrics and Gynecology (ACOG) defines chronic hypertension as hypertension diagnosed or present before pregnancy, or before 20 weeks of gestation [1,2]. The diagnostic criteria used for chronic hypertension in pregnancy have traditionally been two blood pressure readings at least four hours apart with a systolic blood pressure of 140 mmHg or more, a diastolic blood pressure reading of 90 mmHg of more, or both [1]. These criteria were based on previously published American College of Cardiology (ACC) and the American Heart Association (AHA) guidelines for the general population for diagnosing hypertension. Chronic hypertension is associated with increased maternal and neonatal morbidity and mortality and continues to increase in prevalence over time. It is estimated that the rate of chronic hypertension during delivery hospitalizations increased by approximately 80 % from 1995 to 2008, meaning 1.8 % of deliveries were complicated by chronic hypertension. This is expected to continue increasing over time [3]. In 2023, the World Health Organization reported that worldwide, an estimated 1.3 billion adults had hypertension, including one in five females [4,5].

Recently, the ACC and the AHA have modified their criteria to include a systolic blood pressure of 130–139 mmHg, a diastolic blood pressure of 80–89 mmHg, or both to be classified as stage I hypertension [6,7]. In addition, the recommendations now suggest initiating a blood pressure-lowering medication for those with stage I hypertension and clinical cardiovascular disease or a 10-year atherosclerotic cardiovascular disease (ASCVD) risk of 10 % or higher [6,8]. The 2017 ACC/AHA guidelines specifically state that the management of hypertension in pregnancy is beyond its scope. Therefore, there is a paucity of data that assesses the effect that the expansion of the diagnostic criteria of hypertension may have on the diagnosis and treatment of chronic hypertension in pregnant patients. According to one study, the application of the new diagnosis of stage 1 hypertension would add 4.5 million pregnant people who meet criteria for the diagnosis of chronic hypertension [9].

In 2020, a cohort study of over 18,000 patients showed an increased risk of preeclampsia in patients with stage 1 or 2 hypertension diagnosed before 20 weeks gestation [10]. In August of 2021, a similar study was done to compare maternal and neonatal outcomes among patients with normal blood pressure, those with Stage I hypertension based on American College of Cardiology-American Heart Association (ACC-AHA) guidelines, and those with hypertension defined by American College of Obstetricians and Gynecologists (ACOG) criteria. Pregnant individuals with Stage I ACC-AHA hypertension during the first trimester experienced higher rates of preeclampsia, preterm birth, and small-for-gestational-age (SGA) neonates compared to those with normal blood pressure. While adverse maternal and neonatal outcomes were less frequent in the Stage I ACC-AHA group than in the ACOG group, the difference was statistically significant only for preterm birth [11]. Further research is needed to determine the best approach to managing Stage I ACC-AHA hypertension in early pregnancy [7,12,13].

The objective of this study is to compare the rates of preeclampsia between obstetric patients with stage I hypertension and those who are normotensive. Secondary aims include estimating the rate of stage I hypertension among pregnant patients, identifying risk factors for preeclampsia within the cohort of patients with stage I hypertension, and estimating and comparing the rates of other adverse pregnancy outcomes between patients with and without stage I hypertension.