The Treatment of Mild Hypertension in Pregnancy: A New CHAPter

In a recent practice advisory, the American College of Obstetricians and Gynecologists (ACOG) updated guidelines for the treatment of chronic hypertension in pregnancy¹ based upon new data released from the Chronic Hypertension and Pregnancy (CHAP) trial.² ACOG now recommends that clinicians initiate antihypertensive treatment for blood pressure above 140/90 mmHg in pregnancy, replacing the previous threshold of 160/110 mmHg.

Chronic hypertension affects more than 83,000 pregnant women, representing 2.2% of pregnancies in the United States annually.³ Hypertensive disorders of pregnancy portend not only intrapartum and postpartum complications, but also herald increased long-term risk of cardiovascular disease.

Evolving treatment guidelines for hypertension in pregnancy reflect a balance between the risk of fetal harm and the benefit of preventing maternal complications.^4,5 Arguments against tighter blood pressure control include unclear long-term risk to women from short (up to 9 month) exposure to hypertension, risk of placental hypoperfusion and subsequent growth restriction, as well as risk to the fetus from medication exposure. The Control of Hypertension in Pregnancy (CHIPS) trial was designed to address the risk of fetal harm with the treatment of hypertension, finding no statistically significant differences in pregnancy loss, intensive neonatal care, or overall maternal complications with tighter blood pressure control.⁶ Though CHIPS demonstrated no increased risk of fetal harm, the trial was insufficiently powered to evaluate potential maternal benefits of antihypertensive therapy.

Dr. Alan Tita, Professor of Obstetrics and Gynecology and Director at the University of Alabama at Birmingham, and colleagues published the CHAP trial in the New England Journal of Medicine, assessing the potential maternal benefit of tighter blood pressure control in pregnancy. They enrolled a total of 2,408 pregnant women in an open-label, multicenter, randomized trial comparing the treatment of hypertension above 140/80 mmHg (first line recommended therapy was labetalol or extended release nifedipine) versus withholding treatment until the development of severe hypertension (>160/105 mmHg). Tita et al. assessed the composite primary outcome of the development of preeclampsia with severe features, medically indicated preterm birth (<35 weeks gestation), placental abruption, or fetal demise with a safety outcome of fetal growth restriction.

The authors of the CHAP trial should be commended for their enrollment of a diverse group of women, including 48% non-Hispanic Black women and 20% Hispanic women. Tita et al. found a lower incidence of the primary outcome in the active-treatment group compared with the control group (30.2% vs. 37.0%, ARR 0.82, p<0.001), with an estimated number needed-to-treat of 14 to 15 women. These results were driven by the reduction in the incidence of preeclampsia with severe features and preterm birth. As in the CHIPS trial, there was no statistically significant difference in fetal growth restriction between groups.

Dr. Tita commented, “our findings support the benefits and safety of treating women with mild chronic hypertension to a BP goal less than 140/90 mmHg. We applaud SMFM and ACOG for their swift response to the CHAP findings with new guidelines.”

1/2: Today, @MySMFM published, "Antihypertensive therapy for mild chronic hypertension in pregnancy: The CHAP Trial," in @AJOG_thegray. @ACCinTouch #ACC22 @NEJM pic.twitter.com/m2FIt3gq4o

— SMFM (@MySMFM) April 7, 2022

The results of the CHAP trial are remarkable, providing compelling evidence to support changes to guideline recommended treatment of mild chronic hypertension in pregnancy. Future studies may address whether the observed treatment effects extend beyond the peripartum period to reduce long-term cardiovascular morbidity and mortality in women with hypertensive disorders of pregnancy.

In pregnant women with mild chronic hypertension, targeting a blood pressure of < 140/90 mm Hg was associated with better pregnancy outcomes than a strategy of reserving treatment only for severe hypertension. #ACC22 https://t.co/fDrqa8uQiO pic.twitter.com/9KvogjnKcc

— NEJM (@NEJM) April 2, 2022

References

1. The American College of Obstetricians and Gynecologists Committee on Clinical Practice Guidelines. Clinical Guidance for the Integration of the Findings of the Chronic Hypertension and Pregnancy (CHAP) Study. April 2022. https://www.acog.org/clinical/clinical-guidance/practice-advisory/articles/2022/04/clinical-guidance-for-the-integration-of-the-findings-of-the-chronic-hypertension-and-pregnancy-chap-study
2. Tita AT, Szychowski JM, Boggess K, et al. Treatment for mild chronic hypertension during pregnancy. N Engl J Med. DOI: 10.1056/NEJMoa2201295.
3. Greene MF & Williams WW. Treating Hypertension in Pregnancy. N Engl J Med. DOI: 10.1056/NEJMe2203388.
4. Garovic VD, Dechend R, Easterling T, Karumanchi SA, McMurtry Baird S, Magee LA, et al. Hypertension in Pregnancy: Diagnosis, Blood Pressure Goals, and Pharmacotherapy: A Scientific Statement From the American Heart Association. Hypertension. 2022;79(2):e21-e41.
5. Chronic hypertension in pregnancy. ACOG Practice Bulletin No. 203. American College of Obstetricians and Gynecologists. Obstet Gynecol 2019;133:e26-50.
6. Magee LA, Singer J, von Dadelszen P, Group CS. Less-tight versus tight control of hypertension in pregnancy. N Engl J Med. 2015;372(24):2367-8. doi: 10.1056/NEJMc1503870.