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Pre-eclampsia and high blood pressure in pregnancy

A doctor speaks: Pre-eclampsia and why blood pressure is important during pregnancy

In this introduction, Dr Rehan-Uddin Khan (Consultant Obstetrician and Gynaecologist and Director of Medical Education, Barts and the Royal London Hospital) tells us more about pre-eclampsia and why monitoring blood pressure during pregnancy is important.
 
 

Dr Khan explains why blood pressure in pregnancy is important.

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So blood pressure is one of the most important things that we think about in pregnancy. The reason why is because a large number of women will, during the pregnancy, have problems with high blood pressure. Sometimes that’s just high blood pressure on its own and sometimes it’s a disease called pre-eclampsia. We only see this disease in pregnancy but it causes high blood pressure and it leads women to have protein in their urine, which isn’t usually there, sometimes women have swelling. So pre-eclampsia matters because, although many, many women with pre-eclampsia will have a very mild form which won’t affect their own health or the health of their baby, in a way that’s sometimes a little bit difficult to predict, some women will have a more severe form of pre-eclampsia. And when you have severe pre-eclampsia, you can become quite poorly and it’s important for us to try and pick this up. Now, actually, all women have the potential to develop pre-eclampsia and that’s why we check the blood pressure of every woman, pretty much every time we see them during the pregnancy.
 

Dr Khan describes the normal changes to a woman’s blood pressure during pregnancy. Monitoring blood pressure and tracking differences in the readings are important.

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Over the course of a pregnancy, blood pressure does not typically stay absolutely steady. It usually starts at a certain level. During the middle of the pregnancy, it would usually slightly and gently fall. And towards the end of the pregnancy, the blood pressure will slightly and gently rise roughly back to the level where it was at the start. However, we have to track these blood pressure changes by checking blood pressure at each routine check because this is the method by which we work out if, instead of these normal changes, a woman is starting to develop hypertension in pregnancy or pre-eclampsia.
 
When we measure blood pressure, there are two separate numbers. The first is called systolic blood pressure and the second is call diastolic blood pressure. The reason you have to take two separate measurements is because, over the course of one heartbeat, how high or low the pressure is inside a blood vessel changes. When the blood has been forced out from the chambers of the heart into the large blood vessels of the body, the blood pressure initially is relatively high. When the heart muscle subsequently relaxes, so that the chamber can fill up with more blood to be pushed out over the next cycle, the pressure is relatively low. So we look at both numbers because both are important and sometimes we look at the difference between the two.
 

Developing pre-eclampsia can have health risks for both the woman and her unborn baby.

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The vast majority of women will remain relatively well and will end the pregnancy with a healthy baby and a healthy mother but, because the condition is very variable, there are some situations where the mother can become poorly. The problems that mother might have, if they’re not well, can be the following. They might have seizures, the word for which is eclampsia. These can be treated. In very severe cases, the mother might have a stroke. The mother might develop temporary kidney failure, which can be treated. In addition to problems for the mother, because the baby is entirely reliant on the mother’s health, in some cases of pre-eclampsia, the baby can be affected too but again these problems are usually treatable. If the pre-eclampsia is ongoing for a considerable period of time, there are some occasions where the baby might fail to reach his or her growth potential. Doctors call this fetal growth restriction but, once the baby is born, usually, the baby can catch up on what growth has been lost. Sometimes, if the pre-eclampsia is severe before the baby is due, the baby may have to be delivered early.
Risk factors
 
There are several risk factors that mean some women are more likely to develop pre-eclampsia in pregnancy. These factors include:
 
having pre-existing high blood pressure
being overweight
being an ‘older mother’ (usually defined as over the age of 35)
having a family history of high blood pressure or pre-eclampsia in pregnancy. 
 
Risk factors mean there is a higher chance that the woman will develop pre-eclampsia in pregnancy. However, it does not mean that she definitely will, and women without any risk factors may also develop pre-eclampsia.
 

Although some risk factors are known, there is ongoing research into the causes of pre-eclampsia.

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Doctors and scientists have been thinking about high blood pressure in pregnancy for many, many years. We’re still not absolutely sure what the cause is. We know that some women are more likely to get blood pressure problems in pregnancy. For example, women with some medical conditions, women in whom blood pressure problems runs in the family. Women whose mother had pre-eclampsia are more likely themselves to develop pre-eclampsia. But, although we understand it quite well what types of women might be more at risk of pre-eclampsia, in truth, all women can potentially can get pre-eclampsia in pregnancy. There’s been a lot of focus from the scientific community, over the last few decades, about the reasons why women might get pre-eclampsia. We still don’t know for sure but we think there are a lot of factors involved here. Some of them might be inborn factors that women are born with, some might be factors that are acquired over time, for example, a change in weight or having diabetes. We think that there’s probably something which goes wrong at the microscopic level in the ways in which cells interact with each other and pass messages to each other. Blood pressure can go up if blood vessels respond to these messages in certain ways. For example, if the diameter of a blood vessel narrows, that might lead the pressure to rise [phone buzz] and that rising blood pressure then later shows itself as pre-eclampsia.  So there’s going to be a lot of focus in the next few years about why it is that some blood vessels narrow in their diameter. 
Dr Khan recommended that women who are concerned about their risks “ask questions of your midwife, your GP or your obstetrician”. They can advise on any extra checks or surveillance that might be needed in the pregnancy.
 
Different conditions and labels
 
There are different conditions in pregnancy which involve high blood pressure. Examples include ‘pregnancy-induced hypertension’, ‘pre-eclampsia’ and ‘HELLP syndrome’. These conditions are not the same, but they are often thought of as being linked because they all tend to involve high blood pressure in pregnant women. However, blood pressure is not the only feature of these conditions, and some have other signs and symptoms too. 
 

Dr Khan talks here about two conditions associated with blood pressure in pregnancy: pre-eclampsia and pregnancy-induced hypertension. He also says that women with pre-existing high blood pressure are at greater risk of developing pre-eclampsia.

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So there are really perhaps three types of conditions that we can talk about. The first is called pre-eclampsia and in pre-eclampsia women might feel okay or they might feel not well. They will have high blood pressure. They would have protein in the urine and they might well have swelling. Depending on whether or not this is at the mild end of the spectrum or at the severe end of the spectrum, they might have other problems as well potentially affecting different organ system in the body such as the kidneys or the liver or the blood clotting system. If pre-eclampsia is very severe, it can progress to a condition called eclampsia, where women get fits or seizures. The second condition has different names. Some people call it gestational hypertension, some people call it pregnancy induced hypertension and this condition is similar to pre-eclampsia but really the main problem in it is high blood pressure, perhaps not with such a pronounced effect in terms of how much protein you have in your urine or how you feel. And there’s been a lot of interest about whether this crosses over with pre-eclampsia and, in fact, whether it’s a separate condition at all. The third type of condition that we consider is that some women actually fall pregnant having already had a problem with blood pressure. Usually, this has come of its own accord and often women have blood pressure running in their family. Some people all this chronic hypertension. And we have to be quite vigilant about chronic hypertension in pregnancy because, when compared with, if you like, the average woman, a woman with chronic hypertension is more likely to get pre-eclampsia in pregnancy.
 

Dr Khan explains here what HELLP syndrome is, a complication of pregnancy which is thought to be a variant of pre-eclampsia.

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HELLP syndrome is a condition where each letter of the word HELLP stands for a different problem. The H is for haemolysis and haemolysis means red blood cells breaking down and, in some ways, bursting. The EL stands for elevated liver enzymes. The liver is an important organ at all times and, in this particular condition, the liver is affected and that leads to a leakage of the chemicals or the enzymes from the liver into the bloodstream, so when we measure them, the level is higher. There’s a second L before the P and the final LP stands for low platelets. Platelets are one of the three types of cells that we find in blood. They’re particularly important with regards to how blood clots. The level of platelets in HELLP syndrome is lower so, therefore, you have a problem with red cells, a problem with the liver and a problem with the level of platelet cells in the blood.
The different names and labels for various conditions involving high blood pressure in pregnancy can be very confusing. Dr Khan said that sometimes a woman’s diagnosis can shift quite quickly. Changes are identified in her symptoms and test results: “For example, a woman may be diagnosed with pre-eclampsia because she has high blood pressure and protein in the urine but it might be that 48 hours later, she is diagnosed with HELLP syndrome because blood tests show evidence of liver enzymes leaking into the circulation and of changes to the red blood cells knowns as haemolysis and a reduction in the level of platelets. These two diagnoses are not in conflict with each other but demonstrate that pre-eclampsia can progress over time”.
 
 

Dr Khan says there is often confusion about the different labels used when talking about pre-eclampsia or other blood pressure disorders in pregnancy. This is sometimes because the condition progressed over time.

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It can be confusing for women to understand what’s going wrong when different doctors and midwives are using different words. Examples of these words might be hypertension in pregnancy, pre-eclampsia or HELLP syndrome and one of the reasons that sometimes midwives and doctors seem to cross over with these words is because the conditions themselves cross over to a greater or lesser degree. For example, HELLP syndrome, which is a condition where you might have damage to red blood cells, changes in how the liver works and changes in certain cells in the blood or platelets, very often, if not almost always, is associated with high blood pressure. So many doctors and midwives feel that HELLP syndrome is actually a subset of pre-eclampsia. Hypertension in pregnancy, on the other hand, is usually a phrase used to describe just high blood pressure in pregnancy, which can be contrasted against pre-eclampsia, which most people understand as a mixture of high blood pressure, protein in the urine and swelling. In truth, for an individual patient, she might be given a variety of these different phrases or terms at different times but it’s important for that patient to question the doctor, if she doesn’t understand exactly what’s going on.
 

Dr Khan describes when women tend to get pre-eclampsia.

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Most women who are affected by high blood pressure are affected during the latter stages of the pregnancy. The majority of women are therefore affected in what we call the third trimester, which is the last one third of the pregnancy, and sometimes for the first to few days to weeks after they give birth to their child. In a minority of patients, they might be affected earlier but in a lot of these patients it turns out that, actually, they’ve had a blood pressure problem possibly from even before the pregnancy’s beginning.
 
There is a risk of pre-eclampsia after a woman gives birth. Although many women develop evidence of pre-eclampsia before they give birth, in some women pre-eclampsia only comes to light after the delivery but pre-eclampsia remains a condition of pregnancy and soon afterwards. It isn’t a permanent condition and it’s always the case that pre-eclampsia will get better if enough time is given. However, some women continue to need monitoring and treatment for a number of weeks after the birth of their baby.  
For our website, we talked to 41 women and their partners about blood pressure in pregnancy. We heard from a wide range of people whose experiences ranged from one end of a scale (e.g. those who self-monitored their blood pressure as part of a medical study called BuMP and did not go on to develop any high blood pressure problems) through to the middle (e.g. those who were moderately affected by high blood pressure problems) and to the other end of the scale (e.g. those who were severely affected by high blood pressure problems). The number of people spoken to with a particular severity of their experiences is not reflective of the number of cases in the population overall. For example, we interviewed quite a few women who had HELLP syndrome although, as Dr Khan explained, “Pre-eclampsia is a relatively common condition but HELLP syndrome is rare”.
 

Dr Khan talks about the prevalence of high blood pressure disorders in pregnancy. He says that, of these cases, HELLP syndrome is quite a rare condition.

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We estimate that in the UK each year around one in seven women are affected by pre-eclampsia or HELLP syndrome or blood pressure in pregnancy but, within that, very few women are affected by HELLP syndrome, which I think is very much towards the extreme end of these problems. We can’t be exactly sure how many women are affected because different doctors and different scientists use slightly different definitions of pre-eclampsia, but our best guess is probably around one in seven.
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