The American College of Cardiology and American Heart Association (ACC/AHA) updated their blood pressure (BP) criteria in 2017, establishing lower thresholds to identify hypertension in non-pregnant adults. Adoption of these revised standards in pregnant women might allow earlier recognition of individuals at greater risk for complications. This approach holds particular promise for stratifying risk among first-time mothers. The present secondary analysis of the SCOPE cohort evaluated whether these ACC/AHA BP groupings could effectively highlight nulliparous women of standard risk who are predisposed to poorer pregnancy results. Participants were drawn from the international SCOPE cohort and included all pregnancies reaching 20 weeks’ gestation or beyond during the period 2004–2008. The majority of women were White, aged in their twenties, and possessed normal or elevated body mass index (BMI). Cases involving fetal demise prior to 20 weeks or pregnancy termination at any stage were omitted from the dataset. Classification of participants relied on the maximum BP value observed throughout gestation, applying ACC/AHA definitions: normal (BP <120/80 mmHg), “Elevated BP” (120–129 mmHg systolic with <80 mmHg diastolic), “Stage-1 hypertension” (systolic BP [sBP] 130–139 mmHg or diastolic BP [dBP] 80–89 mmHg), and “Stage-2 hypertension” (split into non-severe [sBP 140–159 mmHg or dBP 90–109 mmHg] and severe [sBP ≥160 mmHg or dBP ≥110 mmHg]). Key endpoints comprised preterm birth (PTB), birthweight below the 10th centile, postpartum hemorrhage, and requirement for neonatal unit care. Adjusted relative risks (aRRs) along with diagnostic accuracy measures were determined for each endpoint, both by direct comparison of BP categories to the normal reference group and by treating category boundaries as potential diagnostic cut-points. All models accounted for maternal age, BMI, smoking, ethnicity, and alcohol intake. From the original 5,628 women in the SCOPE study, 5,597 were eligible for inclusion. Severe “Stage 2 hypertension,” relative to normal BP, correlated with markedly elevated occurrence of PTB (24.0% versus 5.3%; aRR 4.88, 95% CI [3.46 to 6.88]), birthweight <10th centile (24.4% versus 8.8%; aRR 2.70 [2.00 to 3.65]), and neonatal unit admission (32.9% versus 8.9%; aRR 3.40 [2.59 to 4.46]). Non-severe “Stage 2 hypertension” likewise showed associations with birthweight <10th centile (16.1% versus 8.8%; aRR 1.82 [1.45 to 2.29]) and neonatal unit admission (15.4% versus 8.9%; aRR 1.65 [1.31 to 2.07]). However, none of the BP categories below “Stage 2 hypertension” demonstrated any significant relationship with the examined adverse events. Assessment of individual BP levels as diagnostic thresholds revealed that only severe “Stage 2 hypertension” generated a strong positive likelihood ratio (LR) of 5.09 (95% CI [3.84 to 6.75]) for predicting PTB. Conversely, no BP cut-off proved effective at excluding the possibility of adverse outcomes, with all negative LRs remaining above 0.2. Important constraints of the work encompass the cohort’s limited ethnic variety, reliance upon BP readings from routine clinical documentation close to delivery, the retrospective approach, inconsistent availability of BP data at every antenatal appointment, and incomplete descriptions of several outcome measures. Findings from this investigation indicate that the 2017 ACC/AHA BP classification system produces analogous associations and predictive characteristics among nulliparous women as those documented in the wider obstetric setting. Thresholds situated below the conventional “Stage 2 hypertension” definition failed to correlate with heightened chances of preterm birth, low birthweight, postpartum hemorrhage, or neonatal unit admission. Consequently, the evidence does not favor incorporating these reduced BP values to signify abnormality in nulliparous pregnancies.
