How blood pressure predicts pregnancy outcomes

According to a recent study published in the American Journal of Obstetrics & Gynecology, adverse pregnancy outcomes can be predicted by blood pressure (BP) thresholds of 140 mm Hg for systolic BP (SBP) and 90 mm Hg for diastolic BP (DBP) at 20 weeks of gestation onward.

Adverse pregnancy outcomes are frequently assessed in pregnant women by measuring BP. The standardized BP thresholds are 140 mm Hg or more for SBP and 90 mm Hg or more for DBP. Chronic hypertension (HTN) is determined by this threshold being met before 20 weeks of gestation, while HTN is gestational when met at 20 weeks or more of gestation.

BP thresholds allow doctors to determine if patients need closer surveillance, further investigation, or treatment. However, continuous BP levels, even below the standardized measures, may impact pregnancy outcomes.

The American College of Cardiology (ACC) and American Heart Association (AHA) recommended lowering BP thresholds for HTN in 2017 to 120/80 mm Hg or more, but these recommendations have not been used in pregnancy HTN guidelines. To determine if the definition of gestational HTN should be updated based on these guidelines, investigators conducted a systematic review.

Databases consulted for the review included PubMed, Embase, Ovid MEDLINE, CINAHL, Latin American and Caribbean Health Sciences Literature, Cochrane Central Register of Controlled Trials, and International Clinical Trials Registry Platform. Evaluation occurred between January 1, 2017, and September 5, 2022.

Studies using 2017 ACC and AHA guidelines to assess BP in pregnancy were gathered. Eligibility criteria included having BP measurements from 20 weeks or more of gestation and evaluating the association between BP measurements and maternal or neonatal outcomes. 

Normal BP was considered SBP of under 120 mm Hg and DBP of under 80 mm Hg, while elevated BP was SBP of 120 to 129 mm Hg and DBP of under 80 mm Hg. Stage 1 HTN was an SBP of 130 to 139 mm Hg or DBP of 80 to 89 mm Hg, while stage 2 HTN was an SBP of 140 mm Hg or more or DBP of 90 mm Hg or more.

Stage 2 HTN was divided into nonsevere (SBP of 140 to 159 mm Hg or DBP of 90 to 109 mm Hg) and severe (SBP of 160 mm Hg or more or DBP of 110 mm Hg or more) categories. Exclusion criteria included being a case report, only reporting mean arterial pressure, and not categorizing BP and presenting it as a continuous variable.

Serious maternal complications, perinatal death, small-for-gestational-age infants, preterm birth, and neonatal intensive care unit (NICU) admission were the primary outcomes of the analysis. Secondary outcomes included maternal death, intensive care unit admission, placental abruption,intubation or ventilation, cesarean delivery, postpartum hemorrhage, neonatal respiratory support, and neonatal seizures.

Three reviewers evaluated search results, with 2 reviewers extracting data. Two reviewers also performed methodological quality assessment using the Quality Assessment of Diagnostic Accuracy Studies 2 tool.

There were 12 studies which met the eligibility criteria, half of which were secondary analyses. Data gathering occurred in the United States in half of the studies, while 1/3 gathered data in low- and middle-income countries. Most studies had a high risk of bias.

Across all 12 studies, there were 251,172 women evaluated, with a median body mass index of 25 and a strong representation of non-Hispanic White and Black populations. Reported BP measurements were often based on a single measurement performed under study conditions, with half of the studies comparing each ACC and AHA BP category with normal BP.

Preeclampsia was reported in a median 4.5% of patients. Of all BP categories, only stage 2 HTN was associated with most adverse pregnancy outcomes, especially preeclampsia. However, while few associations were reported for the 130/80 mm Hg and 120/under 80 mm Hg cutoffs, preeclampsia was also associated with these cutoffs.

No BP threshold was useful as a “rule-out” test, and only stage 2 HTN was useful for preeclampsia, eclampsia, stroke, perinatal death, and NICU admission. While results did not significantly differ based on gestational age group, the strongest associations were at a BP cutoff of 140/90 mm Hg.

These results indicated that lowering the threshold for abnormal BP in the second half of pregnancy from 140/90 mm Hg would not increase accuracy in identifying maternal or perinatal risk in patients. As no threshold could reassure in terms of individual women, investigators recommended BP be measured at each antenatal visit.

Reference

Slade LJ, Wilson M, Mistry HD. The 2017 American College of Cardiology and American Heart Association blood pressure categories in the second half of pregnancy—a systematic review of their association with adverse pregnancy outcomes. American Journal of Obstetrics & Gynecology. 2023;229(2). doi:10.1016/j.ajog.2023.01.013