ObjectiveA relationship between the 2017 American College of Cardiology and American Heart Association blood pressure thresholds and adverse pregnancy outcomes has been reported, but few studies have explored the diagnostic test properties of these cutoffs.Data SourcesWe systematically searched electronic databases (from 2017 to 2021) for reports of blood pressure measurements in pregnancy, classified according to 2017 American College of Cardiology and American Heart Association criteria, and their relationship with pregnancy outcomes.Study Eligibility CriteriaStudies recording blood pressure at <20 weeks gestation were included.MethodsMeta-analyses were used to investigate the strength of the association between blood pressure cutoffs and adverse outcomes, and the diagnostic test properties were calculated.ResultsOf 23 studies included, there was a stepwise relationship between the American College of Cardiology and American Heart Association blood pressure category (when compared with normal blood pressure of <120/80 mmHg) and the strength of the association with preeclampsia. The category of elevated blood pressure had a risk ratio of 2.0 (95% prediction interval, 0.8–4.8), the stage 1 hypertension category had a risk ratio of 3.0 (95% prediction interval, 1.1–8.5), and the stage 2 hypertension category had a risk ratio of 7.9 (95% prediction interval, 1.8–35.1). Between-study variability was related to the magnitude of the association with stronger relationships in larger studies at low risk of bias and with unselected populations with multiple routine blood pressure measurements. None of the systolic blood pressure measurements of <120 mmHg, <130/80 mmHg, or <140/90 mmHg were useful to rule out the development of preeclampsia (all negative likelihood ratios >0.2). Only a blood pressure measurement of ≥140/90 mmHg was a good predictor for the development of preeclampsia (positive likelihood ratio, 5.95). The findings were similar for other outcomes.ConclusionAlthough a blood pressure of 120 to 140 over 80 to 90 mmHg at <20 weeks gestation is associated with a heightened risk for preeclampsia and adverse pregnancy outcomes and may assist in risk prediction in multivariable modelling, lowering the diagnostic threshold for chronic hypertension would not assist clinicians in identifying women at heightened risk.