Critical six-week window to 'reset' blood pressure after giving birth

Lowering a hypertensive mother's blood pressure within six weeks after giving birth could significantly cut their future risk of a heart attack or stroke, according to research funded by the British Heart Foundation and published in Hypertension.

The University of Oxford researchers, who include Oxford University Hospitals (OUH) clinicians, also found that giving women blood pressure monitors and personalised advice led to lower blood pressure in this critical six-week window, and in the four years that followed.

Around one in ten women develop hypertension (high blood pressure) during pregnancy. This significantly increases their risk of long-term high blood pressure, which can lead to a heart attack or stroke.

Elevated blood pressure after pregnancy can cause 'remodelling' of the mother's heart and blood vessels, and so the team were interested in whether controlling high blood pressure in the six weeks after birth could help the mother's heart and blood vessels 'recover' after a pregnancy complicated by high blood pressure.

Acting during this period could thereby 'reset' a woman's blood pressure to pre-pregnancy levels and prevent harmful changes to her heart and circulatory system from becoming permanent.

In an earlier trial, the researchers investigated whether new mothers who monitored their blood pressure at home every day for six weeks after a hypertensive pregnancy would have bigger reductions in their blood pressure, compared to new mothers who received usual care.

They found that women who were given a device to monitor their blood pressure daily and received personalised advice from doctors on adjusting their blood pressure-lowering medication in response to the readings, a process called self-management, had lower blood pressure at six weeks and six months after birth.

Now, four years later, the team have followed up 61 of the women (31 received usual care and 30 were randomised to self-management) to assess the longer-term impact of monitoring their blood pressure. They found that diastolic blood pressure - the blood pressure reading at the point the heart relaxes between beats - was on average 6.8 mmHg lower in women who had self-managed than those who received usual care.

This sustained reduction in blood pressure remained even though the women had stopped taking their blood pressure lowering medication several years earlier.

The researchers estimate that a decrease of 6.8mmHg would reduce the subsequent risk of developing heart and circulatory conditions in future by more than 30 percent. 

Dr Jamie Kitt, a BHF Clinical Research Training Fellow at the University of Oxford's Radcliffe Department of Medicine, led the research.

He said: "High blood pressure during pregnancy leads to additional, adverse changes to the heart, brain and circulatory system due to the increased demands being placed on them.

"After pregnancy, changes to the heart and circulatory system should revert to their pre-pregnancy state. But, when a woman has high blood pressure during pregnancy, many of these changes remain. We're currently running a larger study that will help us to understand more about exactly why these changes occur and why these increase the risk of future poor heart health."

Professor Paul Leeson, Professor of Cardiovascular Medicine at the Radcliffe Department of Medicine and a Consultant Cardiologist at OUH, said: "Current clinical guidelines highlight that women who have had a hypertensive pregnancy are at risk of future heart disease. However, they are not able to give advice on what interventions are available to reduce that risk. Our research has shown that self-monitoring at home can lead to significant improvements in blood pressure after pregnancy in both the short and long term. 

"Further research is in progress to understand whether other interventions during this six-week period may also be of benefit. This work should generate the first evidence-based guidance about the best care and support for women after a hypertensive pregnancy to reduce their risk of developing heart and circulatory disease in future."

Dr Sonya Babu-Narayan, Associate Medical Director at the BHF, said: "High blood pressure affects one in 10 pregnancies and increases the risk that a woman will develop cardiovascular disease during her lifetime. But the opportunity to tackle this risk factor in new mothers is often missed after the birth of their child.

"This research illustrates the importance of providing the right care and support for women in the early weeks and months after giving birth to help them keep their blood pressure in a healthy range. The results are very promising and could lead to important changes in how we treat women who have had high blood pressure during pregnancy.

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