Clinical Guidance for the Integration of the Findings of the Chronic Hypertension and Pregnancy (CHAP) Study

  • Practice Advisory PA
  • April 2022

This Practice Advisory was developed by the American College of Obstetricians and Gynecologists’ Committee on Clinical Practice Guidelines—Obstetrics with the assistance of Anjali J. Kaimal, MD, MAS; Manisha Gandhi, MD; Christian M. Pettker, MD; and Hyagriv Simhan, MD.

On April 2, 2022, the findings from the Chronic Hypertension and Pregnancy (CHAP) Study were published1. In this open-label, multi-center randomized trial, 29,772 patients  were screened and 2,408 pregnant women at 61 centers with singleton gestations and mild chronic hypertension were enrolled prior to 23 weeks' of gestation and randomized to receive antihypertensive therapy at a threshold of 140/90 mm Hg (active treatment) versus no treatment until severe hypertension (SBP>=160 or DBP >= 105) developed (control group). The study found a reduced risk of the primary composite outcome (preeclampsia with severe features, medically indicated preterm birth at less than 35 weeks’ of gestation, placental abruption, or fetal or neonatal death) (30.2% versus 37.0%; adjusted risk ratio [RR], 0.82; 95% CI 0.74-0.92; P<.001). The incidence of birthweight less than the 10th percentile was similar in the groups (11.2% in the active-treatment group and 10.4% in the control group; adjusted RR, 1.04; 95% CI 0.82-1.31; P=.76), as were serious maternal and neonatal complications (2.1% and 2.8%; RR, 0.75; 95% CI 0.45-1.26), and 2.0% and 2.6% (RR, 0.77; 95% CI 0.45-1.30), respectively. 

This study demonstrates that utilizing a treatment threshold of 140/90 for pregnant people with chronic hypertension provides improved outcomes compared to one that initiates treatments only for blood pressures at or above 160/105. In comparison to the prior literature on this topic, strengths of the study include the fact that the majority of enrolled patients had a diagnosis of chronic hypertension on therapy at the time of trial entry (56%) and 41% were enrolled prior to 14 weeks' of gestation. Non-Hispanic Black women made up 48%, Hispanic women 20%, and non-Hispanic White women 28% of the patient population. Notably, less than 50% of participants in each arm were using aspirin. 

Based on these findings, ACOG recommends utilizing 140/90 as the threshold for initiation or titration of medical therapy for chronic hypertension in pregnancy, rather than the previously recommended threshold of 160/1102. For patients on blood pressure medications at the start of pregnancy, in the absence of mitigating factors or side effects, they can be maintained on their medications, rather than discontinuing them and waiting to initiate treatment for blood pressures in the severe range. 

It is important to recognize that this study did not establish a goal blood pressure, but rather used a threshold for treatment of 140/90. In addition, although growth restriction was not significantly different between the treatment and control arms, this study did not establish a blood pressure level below which growth restriction may be a risk. 

Acute, severe, or persistent elevations in blood pressure in the second half of pregnancy warrant further evaluation and a period of observation because of concern for superimposed preeclampsia; in this study, the protocol required exclusion of preeclampsia by clinical diagnostic workup before escalation of medication dose beyond 20 weeks' of gestation. In addition, although in this study treatment did not increase the risk of fetal growth restriction, the baseline risk of fetal growth restriction in patients with chronic hypertension warrants third-trimester ultrasound assessment of fetal growth2

Access the Society for Maternal-Fetal Medicine statement on the CHAP study.

Please contact [email protected] with any questions.


  1. Tita AT, Szychowski JM, Boggess K, Dugoff L, Sibai B, Lawrence K, et al. Treatment for mild chronic hypertension during pregnancy. Chronic Hypertension and Pregnancy (CHAP) Trial Consortium. N Engl J Med. Published online April 2, 2022. doi: 10.1056/NEJMoa2201295
    Article Locations:
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  2. Chronic hypertension in pregnancy. ACOG Practice Bulletin No. 203. American College of Obstetricians and Gynecologists. Obstet Gynecol 2019;133:e26-50. doi: 10.1097/AOG.0000000000003020
    Article Locations:
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