Main findings
This is the first systematic review to our knowledge that investigates the efficacy of CCBs as treatment for Black women with diagnoses of HDP. The striking finding from this review is that there is a paucity of randomised control trials focussed on HDP that publish race or ethnicity of their study participants, Fewer still report outcomes in relation to race or ethnicity, representing a significant gap in evidence in these trials. This is despite the extensive documentation of racial and ethnic differences in cardiovascular health outcomes out with, during and following pregnancy.17-19It is therefore impossible to definitively conclude which anti-hypertensive is most effective for each pregnant ethnic group.
Outside of the context of pregnancy, national guidelines in the U.K. and U.S.A. recommend ethnicity based stratification of first‐line anti-hypertensive agents, with Black patients receiving CCB rather than Angiotensin‐Converting Enzyme inhibitors (ACE-i) as first line management of hypertension, regardless of age.6,20These guidelines are based on data from large randomised control trials, which indicate that CCB are more effective in reducing the risk cardiovascular disease and stroke in Black patients.21-23
Another study by Weir et al found that Black patients required between two and four times the dose of Trandolapril (ACE-i) to obtain a response similar to that observed in White patients.24 A systematic review of hypertension treatment for non-pregnant Black patients concluded that thiazide-like diuretic and CCB monotherapy were better at achieving target blood pressure levels compared with beta-adrenergic blocker, ACE-i or angiotensin receptor blocker (ARB) monotherapy.25These studies demonstrate that it is possible that Black patients may have different responses to certain hypertensive drugs compared to other ethnicities. Black patients are at increased risk of hypertension associated end-organ damage at lower blood pressure levels compared to other ethnicities, and it is therefore essential that anti-hypertensives achieve tight control of blood pressure in this group.26
Previous population studies have demonstrated that chronic hypertension is more prevalent in younger Black women than Black men or women of White ethnicity until 75 years of age.27In particular, Black women are at higher risk for developing refractory hypertension and often require multiple anti-hypertensive drugs for adequate blood pressure control.28-29
Women with HDP are more likely to develop essential hypertension and have an elevated risk of future cardiovascular disease.30-31In fact, it has been shown that the onset of cardiovascular dysfunction can be noted as early as shortly after the index pregnancy affected by HDP.32Black women are known to be particularly at risk of developing HDP.33In one study, women of Black ethnicity with HDP were significantly more likely to require post-partum care in a high dependency unit compared with White women, suggesting a correlation between Black ethnic background and increased disease severity.34 Disparities in socioeconomic status have been theorised as a plausible explanation for these differences35 but these do not account entirely for the variances, given that studies based in free at point-of-care healthcare systems have previously adjusted for deprivation score as a baseline characteristic, and still noted that Black women had significantly worse perinatal outcomes.36-37In another study, Black women were more likely to have had pre-eclampsia in a previous pregnancy compared to other ethnicities regardless of BMI (p=0.014).38They also reported that on any postpartum day, a Black woman with BMI < 35 was 50 percent less likely to achieve resolution of HDP than a non-Black woman in the same BMI category (HR 0.51, 95% CI 0.27–0.95).38The probability of a Black woman with a BMI ≥ 35 achieving blood pressure resolution was 71 percent lower (HR 0.29, 95% CI 0.12–0.74).38This data highlights the potential role of increased severity of maternal disease in Black women with HDP, independent of other risk factors, further strengthening the argument that optimisation of anti-hypertensive treatment in this cohort is crucial in order to ameliorate these clinical discrepancies.
HDP contribute to 2·8 percent, 7·4 percent, and 14 percent of pregnancy related deaths in the U.K., U.S.A. and worldwide respectively.39-41Previous reviews have shown that deaths from HDP are largely preventable, and associated with substandard care.42 The lack of consensus around whether race based differences in first line management of hypertension outside of pregnancy should extend to HDP due to lack of good quality research represents a lack of evidence-based gold standard care, which may contribute to the persistent racial disparities in maternal mortality and morbidity.
This current review highlighted just one randomised control trial, which stratified HDP outcomes by ethnicity. Webster et al commented on some treatment effect by ethnicity in their trial comparing Labetalol with Nifedipine. They reported that Labetalol had a greater effect in reducing mean diastolic blood pressure in non-Black participants. Another article included in this review, which could not be used for meta-analysis due to unavailability of race based outcomes, by Scardo et al is also of interest as 62 percent of its study population was Black, the trial with the highest proportion of Black participants. They demonstrated that Nifedipine was associated with quicker resolution of raised blood pressure. Additionally, the cohort allocated to Nifedipine required fewer doses of anti-hypertensive medication to reach target blood pressure. These two articles in combination support the hypothesis that CCBs could be more effective in the management of HDP in Black patients and that Labetalol, which is the current first-line management of HDP, may not represent the gold standard of treatment in this cohort. It certainly highlights the need for further research in this area.