CHAP backs BP control during pregnancy, even for mild hypertension

Actively treating even mild hypertension to a target blood pressure (BP) of <140/90 mm Hg in pregnant women significantly lowers the risk of adverse pregnancy outcomes without apparent harm to the foetus compared with a strategy of reserving treatment to only when hypertension becomes severe (≥160/105 mm Hg), according to the CHAP* study presented at ACC 2022.

“While there is consensus to treat pregnant women with severe hypertension … it has remained unclear whether to treat pregnant women with mild chronic hypertension,” the investigators pointed out.

“There has been some controversy and uncertainty whether to treat non-severe chronic hypertension during pregnancy, mostly due to concerns that antihypertensive treatment could lead to poor foetal growth,” said lead author Professor Alan Tita from Heersink School of Medicine, University of Alabama at Birmingham in Birmingham, Alabama, US. 

To compound the issue, previous studies have shown conflicting findings on maternal and foetal outcomes with the treatment of non-severe chronic hypertension during pregnancy. Therefore, recommendations for managing non-severe hypertension in pregnant women vary among international guidelines, according to Tita.

“To date, there have been disparate recommendations and hesitancy to treat women with milder forms of high BP during pregnancy for fear of hurting the growing foetus but based on [our] data, doing so may be good for mom and baby,” he said.

Treating to a target BP of <140/90 mm Hg during pregnancy reduced the risk of primary-outcome events — including severe preeclampsia, placental abruption, preterm birth with <35 weeks’ gestation, and foetal or neonatal death — by nearly 20 percent compared with the control strategy (30.2 percent vs 37.0 percent; adjusted risk ratio [RR], 0.82; p<0.001). [N Engl J Med 2022;doi:10.1056/NEJMoa2201295]

Moreover, this benefit did not come with an increase in the incidence of small-for-gestational-age birth weights <10^th percentile — the primary safety outcome — in the active treatment group vs the control group (11.2 percent vs 10.4 percent; RR, 1.04; p= 0.76).

“It was determined that 14 to 15 patients would need to receive active treatment to prevent one primary-outcome event,” the researchers reported.

“After many decades of uncertainty, results of this study support the need for clinical guidance to treat mild as well as severe chronic hypertension in pregnancy and to educate patients about the benefits of doing so,” said Tita.  

CHAP study

The open-label, multicentre trial included 2,408 pregnant women (mean age 32 years) with mild chronic hypertension and singleton foetuses (of <23 weeks’ gestation) who were randomized to receive the recommended antihypertensive treatment to achieve a target BP of <140/90 mm Hg or a control strategy without such treatment unless there was severe hypertension (≥160/105 mm Hg). The recommended antihypertensive agents consisted mainly of labetalol or nifedipine.

More than half of the participants (56 percent) were already taking antihypertensive drug at enrolment, and were allowed to continue on the same medication if they were assigned to the active treatment group.

Rates of the secondary composite outcome of serious maternal complications, although more favourable in the active treatment groups, were not significantly different from the control groups (2.1 percent vs 2.8 percent; RR, 0.75, 95 percent confidence interval [CI], 0.45–1.26), as were for severe neonatal complications (2.0 percent vs 2.6 percent; RR, 0.77, 95 percent CI, 0.45–1.30).

Specifically, the incidence of any preeclampsia (24.4 percent vs 31.1 percent; RR, 0.79, 95 percent CI, 0.69–0.89) and preterm birth (27.5 percent vs 31.4 percent; RR, 0.87; 95 percent CI, 0.77-0.99) occurred in fewer women in the active treatment group than the control group.

Importantly, maternal death was rare overall and occurred at similar rates between the two groups (one in the active treatment group and two in the control group).

“Our findings support the treatment of pregnant women with chronic hypertension with a BP target of less than 140/90 mm Hg, including the continuation of their established antihypertensive therapy,” concluded Tita, who said ACOG** is considering changing their current guidelines in view of these findings.

Plans to continue following up on these women for up to 10 years are ongoing to clarify the long-term effects on cardiovascular health, he pointed out.

*CHAP: Chronic Hypertension and Pregnancy

**ACOG: American College of Obstetricians and Gynecologists