# CHAP (Chronic Hypertension and Pregnancy) trial

Study · id `maternal:chap-trial` · Maternal & Newborn Atlas · release `15708f235d73cd42` (public)

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Also called: CHAP

Browse, life stage: Pregnancy; Newborn  

## In plain language

A large trial in the United States that asked whether women with mildly raised blood pressure before or early in pregnancy do better if they take blood pressure medicine to keep their pressure under 140/90, or if they take medicine only when their pressure becomes severe. Everyone knew which approach they were in.

## Technical summary

Pragmatic, open-label, randomized trial (NCT02299414; phase 4 in the registry). 2408 women were enrolled (the Results text reports 2419 randomized and 2408 analysed). Primary outcome: a composite of pre-eclampsia with severe features, medically indicated preterm birth before 35 weeks, placental abruption, or fetal or neonatal death. Primary safety outcome: a birth weight under the 10th percentile for the baby’s gestational age (small for gestational age). The funder was the National Heart, Lung, and Blood Institute; the registry names the University of Alabama at Birmingham as lead sponsor (no record in this atlas yet). The registry start date (2015-06) and the manuscript’s screening period (from September 2015) differ; the registry date is the one recorded.

## Key facts

- Design: Pragmatic, multicenter, open-label, randomized controlled trial in the United States. Women were randomly assigned either to treatment aimed at keeping blood pressure under 140/90 mm Hg (the active group) or to standard care, in which blood-pressure drugs were not given, or were stopped if already in use, unless severe hypertension appeared. The sample size was reduced from a planned 4700 to a final 2404; the monitoring board for data and safety agreed to the reduction. A blinded outcome adjudication committee reviewed suspected primary and selected secondary outcomes. Follow-up ran to 6 weeks after birth.
- Phase: Phase 4
- Enrolled: 2408 women (enrolled count; Treatment for Mild Chronic Hypertension during Pregnancy, snapshot `maternal:pubmed-35363951-2026-10-11`, retrieved 2026-10-11); 2408 women (registry enrollment, type ACTUAL) (enrolled count; Chronic Hypertension and Pregnancy (CHAP) Project, snapshot `maternal:ctgov-nct02299414-2026-10-11`, retrieved 2026-10-11); 2419 women (randomized count; Treatment for Mild Chronic Hypertension during Pregnancy, snapshot `maternal:pmc-pmc9575330-2026-10-11`, retrieved 2026-10-11); 2404 women (final sample size approved by the data and safety monitoring board) (planned count; Treatment for Mild Chronic Hypertension during Pregnancy, snapshot `maternal:pmc-pmc9575330-2026-10-11`, retrieved 2026-10-11); 4700 women (originally planned enrollment) (planned count; Treatment for Mild Chronic Hypertension during Pregnancy, snapshot `maternal:pmc-pmc9575330-2026-10-11`, retrieved 2026-10-11)
- Started: 2015-06 (actual) (Chronic Hypertension and Pregnancy (CHAP) Project, snapshot `maternal:ctgov-nct02299414-2026-10-11`, retrieved 2026-10-11)
- Primary completion: 2022-04-01 (actual) (Chronic Hypertension and Pregnancy (CHAP) Project, snapshot `maternal:ctgov-nct02299414-2026-10-11`, retrieved 2026-10-11)
- Completion: 2022-12-16 (actual) (Chronic Hypertension and Pregnancy (CHAP) Project, snapshot `maternal:ctgov-nct02299414-2026-10-11`, retrieved 2026-10-11)
- Countries: United States (Chronic Hypertension and Pregnancy (CHAP) Project, snapshot `maternal:ctgov-nct02299414-2026-10-11`, retrieved 2026-10-11)
- Care setting: Recruiting sites of the CHAP Trial Consortium in the United States (more than 70 per the Methods; 2419 women were randomized at 61 sites per the Results). The manuscript does not say whether the sites were clinics or hospitals. (Treatment for Mild Chronic Hypertension during Pregnancy, snapshot `maternal:pmc-pmc9575330-2026-10-11`, retrieved 2026-10-11)
- Registry status: "COMPLETED" (ClinicalTrials.gov (U.S. National Library of Medicine), snapshot `maternal:ctgov-nct02299414-2026-10-11`, retrieved 2026-10-11)

## Study findings

Findings are grouped by the claim they support. Each group keeps its own population and follow-up, and each finding keeps its own denominator and time window. Not reported is not zero.

### In the CHAP trial in the United States, women with mild chronic hypertension who enrolled before 23 weeks of pregnancy and were treated to a blood-pressure goal below 140/90 mm Hg had fewer of the combined serious pregnancy problems than women whose treatment was held back unless their blood pressure became severe. The combined outcome (pre-eclampsia with severe features, a medically indicated preterm birth before 35 weeks, placental abruption, or the death of the fetus or newborn) occurred in 353 of 1170 women with outcome data in the treated group (30.2%) and 427 of 1155 in the control group (37.0%). A separate analysis that fills in missing outcomes gave an adjusted risk ratio of 0.82 (95% CI 0.74 to 0.92).

Claim `maternal:claim-chap-primary-composite`.

Applies to: Recipient: Mixed recipients; Population: The same women as the maternal CHAP context, with the outcomes of their pregnancies. The primary composite combines a maternal event (pre-eclampsia with severe features up to 2 weeks after birth), pregnancy events (medically indicated preterm birth before 35 weeks and placental abruption) and a fetal or neonatal event (fetal or neonatal death). It is used only for the composite as the trial defined it and is never split by recipient.; Care setting: Recruiting sites of the CHAP Trial Consortium in the United States; see the maternal CHAP context.; Geography: United States; Life stage: Pregnancy and the newborn period; Gestational age: Not reported; Postnatal age: Not reported; Follow-up: Pre-eclampsia counted up to 2 weeks after birth. Fetal or neonatal death is listed at under 28 days in the manuscript table; the registry gives up to 90 days for neonatal death.

Limitations: Open-label trial in one country, so women and clinicians knew the assigned strategy. The composite mixes a maternal event with pregnancy events and fetal or neonatal events; the sources do not split it by recipient and the atlas does not either. The percentages and counts come from the complete-case analysis (2325 of 2408 women had enough data); the adjusted risk ratio comes from a multiple-imputation analysis of all 2408. They are different analyses. The authors’ secondary composites of serious maternal complications and of severe neonatal complications did not show clear differences in the abstract; they are about the mother and the newborn separately, so they are not recorded here as claims of their own. Secondary results were not adjusted for multiplicity. For women with newly diagnosed hypertension and for a body-mass index of 40 or more, the risk ratios were close to 1.00 with wide intervals. About 12 women were screened for each woman randomized. The sample size was reduced from a planned 4700 women to a final 2404 that the data and safety monitoring board approved, and the abstract and the Methods word the upper blood-pressure limit differently (below 160/100 vs below 160 and below 105 mm Hg). The registry calls the primary outcome perinatal although it includes a maternal event.

- CHAP primary composite outcome (Primary): Women with a primary-outcome event (count), complete-case analysis 353 women; reported as "353/1170 (30.2%)"; arm Active treatment to a goal below 140/90 mm Hg, no comparator arm; interval Not applicable; denominator 1170 (Complete-case analysis: women with sufficient data on the primary outcome (Table 2 footnote). 1208 women were assigned to the treated group and 1200 to the control group.); time window No single period is stated for the composite. Pre-eclampsia up to 2 weeks after birth; fetal or neonatal death at under 28 days (Table 2 row label). The registry gives up to 90 days for neonatal death.
- CHAP primary composite outcome (Primary): Women with a primary-outcome event (count), complete-case analysis 427 women; reported as "427/1155 (37.0%)"; arm Standard (control) treatment, no comparator arm; interval Not applicable; denominator 1155 (Complete-case analysis: women with sufficient data on the primary outcome (Table 2 footnote). 1208 women were assigned to the treated group and 1200 to the control group.); time window No single period is stated for the composite. Pre-eclampsia up to 2 weeks after birth; fetal or neonatal death at under 28 days (Table 2 row label). The registry gives up to 90 days for neonatal death.
- CHAP primary composite outcome (Primary): Adjusted risk ratio, active treatment vs control (multiple imputation analysis with multivariable log-binomial regression, N = 2408; Table 2 footnote) 0.82 ratio; reported as "0.82 (0.74-0.92), P<0.001"; arm Active treatment to a goal below 140/90 mm Hg compared with Standard (control) treatment; interval 0.74 to 0.92 (95% confidence interval); denominator Not applicable (basis: Imputation analysis of all 2408 women analysed, not the complete-case counts above (Table 2 headings)); time window No single period is stated for the composite. Pre-eclampsia up to 2 weeks after birth; fetal or neonatal death at under 28 days (Table 2 row label). The registry gives up to 90 days for neonatal death.

### In CHAP the mothers were treated, and the safety question was the baby’s growth. Babies born small for their gestational age (birth weight below the 10th percentile) numbered 128 of 1146 with data in the treated group (11.2%) and 117 of 1124 in the control group (10.4%). The adjusted risk ratio was 1.04 (95% CI 0.82 to 1.31). The interval includes no difference, so the trial did not show a clear change in this safety outcome.

Claim `maternal:claim-chap-sga-safety`.

Applies to: Recipient: Newborn; Population: Infants born to the women in the trial who had birth-weight data: 1146 in the treated group and 1124 in the control group in the complete-case analysis. The infants were exposed through their mothers’ treatment; they were not treated themselves. The women enrolled before 23 weeks, and the gestational age at birth was not restricted by the source.; Care setting: Births at CHAP sites in the United States; the manuscript does not describe the birth setting.; Geography: United States; Life stage: Newborn, birth weight measured at birth; Gestational age: Not reported; Postnatal age: 0 days to 0 days; Follow-up: Birth weight at birth. Only the complete-case analysis has a count of infants; the adjusted analysis imputes missing values.

Limitations: The trial was powered to detect a relative difference of 35% or more in small-for-gestational-age birth weight, so a smaller increase cannot be ruled out. The percentages come from the 2270 patients with sufficient data (complete-case analysis of the safety outcome); the adjusted risk ratio comes from a multiple-imputation analysis of all 2408 patients (Table 2, N = 2408). Open-label design, one country. The recipient is the newborn, exposed through the mother’s treatment.

- Small-for-gestational-age birth weight (CHAP safety outcome) (Primary): Infants with birth weight below the 10th percentile (count), complete-case analysis 128 infants; reported as "128/1146 (11.2%)"; arm Active treatment to a goal below 140/90 mm Hg, no comparator arm; interval Not applicable; denominator 1146 (Complete-case analysis: infants with sufficient birth-weight data (Table 2 footnote). 1208 women were assigned to the treated group and 1200 to the control group.); time window Birth
- Small-for-gestational-age birth weight (CHAP safety outcome) (Primary): Infants with birth weight below the 10th percentile (count), complete-case analysis 117 infants; reported as "117/1124 (10.4%)"; arm Standard (control) treatment, no comparator arm; interval Not applicable; denominator 1124 (Complete-case analysis: infants with sufficient birth-weight data (Table 2 footnote). 1208 women were assigned to the treated group and 1200 to the control group.); time window Birth
- Small-for-gestational-age birth weight (CHAP safety outcome) (Primary): Adjusted risk ratio, active treatment vs control (multiple imputation analysis with multivariable log-binomial regression, N = 2408; Table 2 footnote) 1.04 ratio; reported as "1.04 (0.82-1.31), P = 0.76"; arm Active treatment to a goal below 140/90 mm Hg compared with Standard (control) treatment; interval 0.82 to 1.31 (95% confidence interval); denominator Not applicable (basis: Imputation analysis of all 2408 patients (Table 2, N = 2408), not the complete-case counts above (Table 2 headings)); time window Birth

### In the CHAP trial, any pre-eclampsia (with or without severe features) occurred in 295 of 1208 women in the treated group (24.4%) and 373 of 1200 women in the control group (31.1%), a risk ratio of 0.79 (95% CI 0.69 to 0.89).

Claim `maternal:claim-chap-any-preeclampsia`.

Applies to: Recipient: Maternal; Population: Pregnant women with known or new chronic hypertension and a viable singleton fetus before 23 weeks of gestation. Mild means below the severe thresholds, but the sources word the limit differently. The abstract says blood pressure below 160/100 mm Hg. The Methods required, at randomization, a systolic pressure of 140 to 159 or a diastolic pressure of 90 to 104 mm Hg for patients who “had not received an antihypertensive drug within 24 hours before measurement”, and below 160 and below 105 mm Hg for patients who “had been receiving antihypertensive therapy”. Women with lower pressures were also eligible. The registry gives a minimum age of 12 years and adds that the minimum age varies by center; the manuscript states no age limit.; Care setting: Recruiting sites of the CHAP Trial Consortium in the United States. The Methods say more than 70 recruiting sites; the Results say 2419 women were randomized at 61 sites. The manuscript does not say whether the sites were clinics or hospitals.; Geography: United States; Life stage: Pregnancy, enrolled before 23 weeks of gestation and followed until 6 weeks after birth; Gestational age: up to 22 weeks 6 days (160 days); Postnatal age: Not reported; Follow-up: Followed until 6 weeks after birth. Pre-eclampsia in the primary composite counted up to 2 weeks after birth.

Limitations: This is a secondary outcome, reported without adjustment for multiplicity, so the authors say it should not be used to infer definitive effects. The risk ratio is not described as adjusted in the abstract or the table. The time window for this outcome is not stated in the manuscript text (follow-up ran to 6 weeks after birth; the primary composite counted pre-eclampsia up to 2 weeks after birth). It overlaps with the severe-features part of the primary composite, so the two must not be added. Open-label design, one country.

- Any pre-eclampsia (CHAP definition) (Secondary): Women with any pre-eclampsia (count) 295 women; reported as "295 (24.4%)"; arm Active treatment to a goal below 140/90 mm Hg, no comparator arm; interval Not applicable; denominator 1208 (All women assigned to the treated group (Table 3 column heading, N = 1208).); time window Not stated for this outcome in the manuscript text
- Any pre-eclampsia (CHAP definition) (Secondary): Women with any pre-eclampsia (count) 373 women; reported as "373 (31.1%)"; arm Standard (control) treatment, no comparator arm; interval Not applicable; denominator 1200 (All women assigned to the control group (Table 3 column heading, N = 1200).); time window Not stated for this outcome in the manuscript text
- Any pre-eclampsia (CHAP definition) (Secondary): Risk ratio, active treatment vs control (Table 3 treatment effect; the table footnote says it is a risk ratio and the abstract does not call it adjusted) 0.79 ratio; reported as "0.79 (0.69 to 0.89)"; arm Active treatment to a goal below 140/90 mm Hg compared with Standard (control) treatment; interval 0.69 to 0.89 (95% confidence interval); denominator Not applicable (basis: Comparison of the two per-arm rows above); time window Not stated for this outcome in the manuscript text

## Connected pages

- Tests a blood-pressure goal below 140/90 mm Hg against treating only severe hypertension: Antihypertensive drug treatment for non-severe hypertension in pregnancy (`maternal:antihypertensive-treatment-non-severe-hypertension-pregnancy`)
- Enrolled women with mild chronic hypertension: Chronic hypertension in pregnancy (`maternal:chronic-hypertension-in-pregnancy`)
- Pre-eclampsia is part of the primary composite and a secondary outcome: Pre-eclampsia (`maternal:preeclampsia`)
- Funder (abstract funding statement): National Heart, Lung, and Blood Institute (NHLBI) (`maternal:nhlbi`)
- Primary results, NEJM 2022: CHAP primary results, NEJM 2022 (`maternal:pub-chap-nejm-2022`)

## Provenance

Content hash: 55158f7ec3a5ca54f0f81cf6128a216380fe98ed5335083a98cbddfc01626c57
Last substantive edit: 2026-10-11
Evidence last checked: Not recorded