Estimated Impact of the 2017 American College of Cardiology/American Heart Association Blood Pressure Guidelines on Reproductive-Aged Women

Abstract

The 2017 American College of Cardiology/American Heart Association (ACC/AHA) Guideline for the Prevention, Detection, Evaluation and Management of High Blood Pressure in Adults lowered the threshold of hypertension compared to the American College of Obstetricians and Gynecologists (ACOG) guidelines used to define hypertensive disorders of pregnancy. We sought to describe the impact of reclassifying hypertension for reproductive-aged women in the United States using the 2017 ACC/AHA guidelines. We analyzed data from a cohort of women 20–44 years of age from the 2011–2014 National Health and Nutrition Examination Survey (n=2311), and sampling weights were used to obtain nationally-representative hypertension prevalence estimates. Additional analyses were performed on subgroups of low-risk women (n=2110) and those currently or previously pregnant (n=1298). The prevalence of hypertension by ACOG and 2017 ACC/AHA guidelines was 10.2% (95% CI, 8.7%−11.6%) and 18.9% (95% CI, 16.8%−21.1%), respectively. Results were similar in a cohort of low-risk women were currently or previously pregnant. This study suggests that adoption of ACC/AHA guidelines for hypertension would increase the number of reproductive-aged women with hypertension by approximately two-fold. Further studies are needed to determine the safety and efficacy of lower blood pressure targets, as well as the potential impact on risk assessment and obstetric care, in this specialized population.

Summary

Approximately twice as many women of reproductive age will have a diagnosis of hypertension by 2017 ACC/AHA guidelines compared to ACOG guidelines.

Introduction

Updated guidelines on the prevention and treatment of hypertension by the American College of Cardiology / American Heart Association (ACC/AHA) defines hypertension as blood pressure (BP) ≥ 130/80 mm Hg – lower than the previous threshold of BP ≥ 140/90 mm Hg.¹ Studies suggest a substantial increase in the prevalence of hypertension in the United States, especially among young, low-risk individuals.² While reproductive-aged women are typically among the lowest risk groups for cardiovascular disease, in those who become pregnant, redefining hypertension may have a significant impact on obstetric care and understanding the maternal-fetal risks associated with hypertension.

Currently, hypertensive disorders of pregnancy (HDP) affect up to 10% of all pregnancies in the United States and are associated with adverse outcomes and increased cost.^3,4 The American College of Obstetricians and Gynecologists (ACOG) defines hypertension in pregnancy as BP ≥ 140/90 mm Hg.³ We sought to describe the impact of reclassifying hypertension for reproductive-aged women in the United States using the 2017 ACC/AHA guidelines.

Methods

All data used in this study have been made publicly available at the Centers for Disease Control and Prevention and can be accessed at https://www.cdc.gov/nchs/nhanes/index.htm.

We analyzed cross-sectional data from noninstitutionalized women 20–44 years of age from the 2011–2012 and 2013–2014 waves of the National Health and Nutrition Examination Survey (NHANES).⁵ This study was considered exempt by the Emory institutional review board, and written informed consent was previously obtained from all participants by NHANES.

Three consecutive BP readings were obtained from participants in a seated position after 5 minutes of rest, and in participants with at least two measurements, mean values were used to define systolic blood pressure (SBP) and diastolic blood pressure (DBP). Hypertension was defined as SBP ≥ 140 mm Hg or DBP ≥ 90 mm Hg for ACOG guidelines,³ and SBP ≥ 130 mm Hg or DBP ≥ 80 mm Hg for 2017 ACC/AHA guidelines.¹ Participants on antihypertensive medication were considered to have hypertension by both guidelines, irrespective of SBP or DBP. Current pregnancy was determined by positive lab pregnancy test or an affirmative response to the question “Are you pregnant now?” and history of pregnancy was determined by self-report. Sociodemographic information and history of cardiovascular disease (CVD), cancer and diabetes were determined by self-report. Obesity was defined as body mass index ≥ 30.

NHANES sampling weights were used to obtain nationally representative prevalence estimates, and current population tables were used to estimate the number of women reclassified as having hypertension.⁶

Results

Of 2311 participants, the mean age was 31.9 years (SE, 0.4), 57.1% were non-Hispanic white and 67.6% were currently or previously pregnant in weighted analyses. The prevalence of hypertension by ACOG and 2017 ACC/AHA guidelines was 10.2% (95% CI, 8.7%−11.6%) and 18.9% (95% CI, 16.8%−21.1%), respectively (Figure). Using current population estimates, an additional 4.5 million women aged 20–44 years had hypertension by 2017 ACC/AHA guidelines compared to ACOG guidelines. The relative increase in hypertension by 2017 ACC/AHA guidelines was consistent across strata of age, race/ethnicity and family income; however, in women with a history of diabetes, CVD or cancer, differences in hypertension prevalence by ACOG and 2017 ACC/AHA guidelines were reduced (Figure).

Figure. Prevalence of Hypertension in Women Age 20–44 Years by ACOG and 2017 ACC/AHA Guidelines.

Estimated prevalence of hypertension by ACOG (light gray bar) and 2017 ACC/AHA (full bar height) guidelines for U.S. women 20–44 years of age. Previous pregnancy was determined by an affirmative response to the question “Have you ever been pregnant?” Obesity was defined as a body mass index ≥ 30 kg/m². Abbreviations: ACOG = American College of Obstetricians and Gynecologists; ACC/AHA = American College of Cardiology / American Heart Association; NH = non-Hispanic; CVD = cardiovascular disease

Subgroup analysis was performed to approximate a low-risk cohort of women with current or previous pregnancy. After excluding high-risk individuals with a history of diabetes, CVD or cancer (N=201), the prevalence of hypertension by ACOG and 2017 ACC/AHA guidelines was 8.2% (95% CI, 6.7%−9.7%) and 17.1% (95% CI, 14.7%−19.5%), respectively (Table). Further exclusion of individuals without a previous or current pregnancy (N=812) resulted in a final cohort of 1298 low-risk, formerly or currently pregnant women who had a prevalence of hypertension by ACOG guidelines of 10.0% (95% CI, 8.1%−11.9%), and by 2017 ACC/AHA guidelines of 20.8% (95% CI, 18.0%−23.6%). The observed two-fold increase in hypertension persisted in all sociodemographic strata (Table).

Table.

Prevalence of Hypertension by ACOG and 2017 ACC/AHA Guidelines for Low-Risk Reproductive-Aged Women in the United States, 2011–2014

	Prevalence of Hypertension, % (95% CI)
	Women*, age 20–44 (n = 2110)		Women*, age 20–44, previously or currently pregnant† (n = 1298)
Characteristic	2017 ACC/AHA Guideline	ACOG Guideline	2017 ACC/AHA Guideline	ACOG Guideline
Overall	17.1 (14.7–19.5)	8.2 (6.7–9.7)	20.8 (18.0–23.6)	10.0 (8.1–11.9)
Age, y
20–34	10.1 (7.6–12.6)	3.6 (2.6–4.7)	11.9 (8.4–15.4)	4.3 (2.8–5.8)
35–44	28.7 (25.1–32.3)	15.7 (12.8–18.7)	30.8 (27.0–34.7)	16.4 (13.5–19.3)
Race/Ethnicity
Non-Hispanic white	16.8 (13.2–20.3)	7.2 (4.9–9.5)	21.6 (16.8–23.4)	8.7 (5.6–11.9)
Non-Hispanic black	27.2 (22.7–31.6)	16.8 (13.7–19.9)	30.1 (24.4–35.8)	19.8 (15.6–24.1)
Non-Hispanic Asian	10.3 (6.2–14.3)	5.0 (2.8–7.2)	12.2 (6.7–17.6)	6.3 (2.6–9.9)
Hispanic or Mexican American	12.0 (8.7–15.4)	6.3 (4.0–8.5)	12.6 (8.6–16.5)	6.6 (3.8–9.3)
Annual family income, $
< 25,000	15.6 (12.8–18.4)	7.3 (5.3–9.2)	19.8 (15.2–24.4)	10.1 (7.5–12.6)
25,000 – 65,000	17.8 (13.9–21.7)	8.9 (7.0–10.8)	21.5 (16.3–26.7)	11.3 (8.0–14.6)
≥ 65,000	17.2 (13.4–20.9)	8.3 (5.2–11.4)	20.7 (15.8–25.6)	8.8 (5.3–12.4)
Obese‡	28.6 (25.0–32.2)	15.4 (12.6–18.2)	31.9 (28.2–35.6)	17.4 (14.3–20.6)
Previously pregnant†	20.8 (18.0–23.7)	9.9 (8.0–11.9)	NA	NA

^*Excludes women with self-reported diabetes, cardiovascular disease or cancer.

^†Current pregnancy was determined by positive lab pregnancy test or an affirmative response to the question “Are you pregnant now?”; previous pregnancy was determined by an affirmative response to the question “Have you ever been pregnant?”

^‡Body mass index ≥ 30 kg/m²

Abbreviations: ACOG = American College of Obstetricians and Gynecologists; ACC/AHA = American College of Cardiology / American Heart Association; CI = confidence interval; NA = not applicable

Discussion

Approximately twice as many reproductive-aged women will have hypertension by 2017 ACC/AHA guidelines compared to previous definitions of hypertension. These differences persist within a subset of low-risk women with a history of pregnancy. While these estimates approximate the burden of chronic hypertension only, the prevalence of other HDP, including preeclampsia, may also increase if the 2017 ACC/AHA definition of hypertension is adopted during pregnancy.

Concurrent with the publication of the 2017 ACC/AHA hypertension guidelines, Muntner et al. showed that, although the prevalence of hypertension among adults in the United States would increase by approximately 31 million people, only 4 million of those individuals would be newly recommended for antihypertensive medication.² The implication that new BP thresholds for hypertension should not necessarily equate to large-scale increases in medication use was especially notable in young, otherwise-healthy people; however, for women of reproductive age who become pregnant, a lower threshold for defining HDP may have significant implications for both obstetric management and risk assessment in the antepartum, intrapartum and postpartum periods.

Maternal mortality has increased to a rate of 17.3 pregnancy-related deaths per 100,000 live births in 2013.⁷ And while the proportion of maternal deaths from HDP has decreased overall, other pregnancy-related mortality rates affected by hypertension, including stroke, have increased.⁸ Importantly, hypertension remains a major risk factor for stroke in pregnancy, as women with HDP are five times more likely to have a stroke than normotensive women, and their rate of stroke-related complications is substantially higher.⁹ Because all HDP are associated with an increased risk of CVD,^10–13 pregnant women with a diagnosis of chronic hypertension often have more frequent office visits and additional screening tests for various maternal-fetal complications, such as preeclampsia and intrauterine fetal growth restriction.^3,14 This increase in resource utilization leads to increased healthcare costs -- deliveries complicated by HDP cost an estimated 25% to 385% more than uncomplicated deliveries.⁴

Furthermore, it is unclear whether lowering the BP threshold for the diagnosis of HDP would significantly affect risk assessment for adverse outcomes in pregnancy. Most studies demonstrating an association between HDP and maternal-fetal complications or future CVD use hypertension as a binary variable and infrequently report actual blood pressure measurements. However, two studies from the Kaiser Permanente health system in California showed that BP 120–130/80–89 mm Hg during pregnancy was associated with a 2-fold increase in subsequent HDP.^15,16 Recently, Youngstrom et al. demonstrated that women with “controlled” chronic hypertension, defined as BP < 140/90 prior to 20 weeks gestation, were at increased risk of fetal complications and preeclampsia, irrespective of antihypertensive use.¹⁷ These findings are compelling and suggest that lower BP thresholds for HDP may result in better, earlier risk assessment in pregnant women.

Lastly, it is still unknown whether treatment to lower BP levels during pregnancy is beneficial. For women with a history of hypertension, tight (DBP < 85 mm Hg) versus loose (DBP < 100 mm Hg) blood pressure control during pregnancy was associated with less severe maternal hypertension and no change in outcomes for the fetus.¹⁸ This is supported by findings from a recent systematic review and meta-analysis that showed antihypertensive therapy was associated with reduced rates of severe maternal hypertension, while results for other maternal-fetal outcomes were either mixed or null.¹⁹ There is even less guidance regarding specific antihypertensive therapies, as head-to-head trials are limited.¹⁹ The 2017 ACC/AHA guidelines specifically reference the paucity of data “on whether treatment of hypertension during pregnancy mitigates risk” and calls for more research to determine if lower BP targets are safe and/or associated with improved maternal-fetal outcomes.¹ However, there may be benefits to lower BP targets for women with HDP beyond consideration for antihypertensive therapy. ACOG guidelines recommend low-dose aspirin to prevent superimposed preeclampsia in pregnant women with chronic hypertension. Hauspurg et al. recently showed that women with stage 1 hypertension by 2017 ACC/AHA guidelines (BP 130–139/80–89 mm Hg) had a significantly reduced risk of preeclampsia with low-dose aspirin therapy compared to normotensive controls.²⁰ Further investigation is needed to determine the utility of targeting lower BP for medical therapy in women with HDP.

Perspectives

The current study demonstrates that adoption of the 2017 ACC/AHA guideline definition for hypertension would approximately double the prevalence of hypertension in women of reproductive age. If ACOG were to adopt the 2017 ACC/AHA definition of hypertension, a similar increase in the prevalence of HDP would be expected. Further research is needed to determine if lower BP thresholds are safe and effective in reducing maternal and/or fetal complications related to HDP.

Novelty and Significance

What is New?

• An additional 4.5 million women of reproductive age will have a diagnosis of hypertension by 2017 ACC/AHA guidelines compared to ACOG guidelines.

• The approximate doubling of hypertension prevalence in reproductive-aged women extends to a cohort of low-risk women with current or previous pregnancy.

What is Relevant?

• If 2017 ACC/AHA definition for hypertension is adopted by ACOG, the burden of pregnant women with a diagnosis of chronic hypertension will increase substantially.

• Further study is needed to determine if lower BP targets in pregnant women are safe, effective and associated with improved outcomes.