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1. Hypertension in pregnant young adults: a balancing act?
Hypertension starts to emerge early in life with between 20 and 40% of people under 45 years old classed as having elevated blood pressure, or hypertension, based on recent guidelines.1 By young adulthood blood pressure is associated with cardiac and brain changes2,3 and reliably predicts risk of future acute vascular events4 but the benefits of blood pressure control at this age continues to be debated. Interventions are often limited to lifestyle advice5 unless significant end organ damage is evident or blood pressure levels are very high.1 As a result, young adults with stage 1 hypertension, meaning blood pressures are between 140 and 160 mmHg systolic and/or 90 and 100 mmHg diastolic, usually remain pharmacologically untreated. So what happens when that young adult falls pregnant? Should pregnancy change our attitude to risk?
Infographic to summarise the design and results of two major clinical trials that have investigated impact of blood pressure control during pregnancy on maternal and fetal outcomes in young people with pre-existing hypertension who become pregnant.
A major difference is that any decisions about blood pressure control need to take into account both the needs of the mother and developing fetus. Fetal wellbeing is dependent on placental perfusion, which in turn is dependent on maternal cardiac output, so interventions to reduce maternal blood pressure could impact the fetus.6 Understandably, this has traditionally resulted in caution about blood pressure treatment until there is evidence of significant problems with the pregnancy or very high blood pressure levels. Arguing against this approach is the extensive observational data that associates elevated blood pressure in pregnancy, even relatively mild elevations, with a range of adverse fetal and maternal outcomes including fetal growth restriction, preterm birth, pregnancy loss and progression to preeclampsia, maternal seizures, organ failure, and mortality.7
2. Chronic Hypertension in Pregnancy Project and The Control of Hypertension in Pregnancy Study
Two randomized studies are now available to inform this academic and clinical debate (Figure 1). The Control of Hypertension in Pregnancy Study (CHIPS)6 was published in 2015 and addressed an initial question of whether reducing blood pressure in pregnancy has an adverse impact on fetal outcome. This ‘safety’ trial enrolled 987 pregnant women across different countries who had pre-existing mild hypertension characterized as an office diastolic blood pressure of between 90 to 105 mmHg. They were randomized to tight control (target diastolic blood pressure below 85 mmHg) vs. less-tight control (target diastolic blood pressure below 100 mmHg) with a primary outcome of pregnancy loss or need for high-level neonatal care. No differences were found in primary outcome nor in secondary outcomes of maternal complications despite a 4.6 mmHg (95% CI, 3.7–5.4) lower diastolic pressure in the intervention arm.
Building on the reassurance provided by this trial, the Chronic Hypertension in Pregnancy Project (CHAP)8, which was published earlier this year, has now tested further questions. The trial focused on whether blood pressure control could beneficially change outcomes for mothers and their baby. 2480 women were recruited across 61 US hospitals, with pre-existing hypertension before 23 weeks gestation, defined as blood pressures between 140 and 160 mmHg systolic or 90 and 105 mmHg diastolic. Fifty percent of those enrolled had a black ethnicity, consistent with real world experience of hypertension in young people.8 Participants were randomized to usual care or medication to reduce blood pressure below 140 mmHg systolic and 90 mmHg diastolic. Those whose blood pressure was treated had significant reductions in the primary outcome, which was a combination of preeclampsia with severe features, medically indicated preterm birth at less than 35 weeks gestation, placental abruption or fetal or neonatal death. A large driver of the change in primary outcome was reduction in severe preeclampsia and preterm birth.
3. Next questions for pregnancy blood pressure trials
CHAP and CHIPS should lead to a new confidence in blood pressure management for young adults with hypertension who become pregnant. There is now clear evidence that maintaining blood pressure levels below 140/90 mmHg during pregnancy can improve both maternal and fetal outcomes. Nevertheless, there were still relatively high event rates in the intervention arm and further questions remain. How soon should blood pressure control be started? If begun pre-conception or early in pregnancy does this improve outcomes? What are the optimal medications for blood pressure control in pregnancy? Does blood pressure control during pregnancy have benefits after pregnancy? Women who have severe hypertension during pregnancy have a significantly increased risk of future cardiovascular disease and recent trials have shown a striking impact of short term interventions during the post-partum period on blood pressure levels for years after pregnancy.9 Furthermore, both hypertensive pregnancy and preterm birth are associated with hypertension and cardiovascular disease in the offspring and there may be cardiovascular benefits for the child of reducing incidence of preterm birth.10 Therefore, expect more trials and investigations. As a result, better guidelines and improved health outcomes for mothers and their children should emerge, which could change the life course of whole families.
References
Author
Biography: Paul Leeson is Professor of Cardiovascular Medicine at the University of Oxford and Head of the Oxford Cardiovascular Clinical Research Facility, as well as being a Consultant Cardiologist at the John Radcliffe Hospital. His research group has pioneered use of imaging and artificial intelligence within observational studies and clinical trials to investigate cardiovascular disease development, in both mother and child, after pregnancies complicated by hypertension. The work has led to innovations in imaging diagnostics as well as evidence that interventions around the time of pregnancy can have long term benefits for maternal health.
Author notes
Conflict of interest: None declared.
