AbstractObjectiveTo examine the association with adverse pregnancy outcomes of: (1) American College of Cardiology/American Heart Association blood pressure (BP) thresholds, and (2) visit‐to‐visit BP variability (BPV), adjusted for BP level.DesignAn observational study.SettingAnalysis of data from the population‐based UK Southampton Women's Survey (SWS).Population or sample3003 SWS participants.MethodsGeneralised estimating equations were used to estimate crude and adjusted relative risks (RRs) of adverse pregnancy outcomes by BP thresholds, and by BPV (as standard deviation [SD], average real variability [ARV] and variability independent of the mean [VIM]). Likelihood ratios (LRs) were calculated to evaluate diagnostic test properties, for BP at or above a threshold, compared with those below.Main outcome measuresGestational hypertension, severe hypertension, pre‐eclampsia, preterm birth (PTB), small‐for‐gestational‐age (SGA) infants, neonatal intensive care unit (NICU) admission.ResultsA median of 11 BP measurements were included per participant. For BP at ≥20 weeks’ gestation, higher BP was associated with more adverse pregnancy outcomes; however, only BP <140/90 mmHg was a good rule‐out test (negative LR <0.20) for pre‐eclampsia and BP ≥140/90 mmHg a good rule‐in test (positive LR >8.00) for the condition. BP ≥160/110 mmHg could rule‐in PTB, SGA infants and NICU admission (positive LR >5.0). Higher BPV (by SD, ARV, or VIM) was associated with gestational hypertension, severe hypertension, pre‐eclampsia, PTB, SGA and NICU admission (adjusted RRs 1.05–1.39).ConclusionsWhile our findings do not support lowering the BP threshold for pregnancy hypertension, they suggest BPV could be useful to identify elevated risk of adverse outcomes.