Pregnancy and High Blood Pressure

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If you are pregnant you should have regular blood pressure checks. Most women will not develop any problems with their blood pressure during pregnancy. However, in some women, high blood pressure (hypertension) can develop. It is often mild and not serious. But in some cases, high blood pressure can become severe and can be harmful to both the mother and baby. Some women with high blood pressure during pregnancy develop pre-eclampsia which is a more serious condition. (There is a separate leaflet dealing with pre-eclampsia.)

High blood pressure (hypertension) means that the pressure of the blood in your artery blood vessels is too high. Blood pressure is recorded as two figures. For example, 140/85 mm Hg. This is said as 140 over 85. Blood pressure is measured in millimetres of mercury (mm Hg). The first (or top) number is your systolic blood pressure. This is the pressure in your arteries when your heart contracts. The second (or bottom) number is your diastolic blood pressure. This is the pressure in your arteries when your heart rests between each heartbeat.

Normal blood pressure is below 140/90 mm Hg. During pregnancy:

  • Mildly high blood pressure is blood pressure between 140/90 and 149/99 mm Hg.
  • Moderately high blood pressure is blood pressure between 150/100 and 159/109 mm Hg.
  • Severely high blood pressure is blood pressure of 160/110 mm Hg or higher.

Pre-existing high blood pressure

Some women already have high blood pressure (hypertension) before they become pregnant and they may be on treatment for this. Some women are found to have high blood pressure before they are 20 weeks pregnant. (If high blood pressure is first discovered before you are 20 weeks pregnant, this usually means that you had previously undetected high blood pressure before you were pregnant.)

So, high blood pressure before 20 weeks of pregnancy is not caused by pregnancy but is pre-existing, or chronic, high blood pressure. Up to 1 in 20 women have pre-existing high blood pressure when they become pregnant. There are various causes. See the separate leaflet called High Blood Pressure (Hypertension) for more details.

If you have pre-existing high blood pressure, you have an increased risk of developing pre-eclampsia during your pregnancy (see below).

Note: if you are taking medicines to treat high blood pressure then, ideally, you should have this reviewed before you become pregnant. Some medicines that are used to treat high blood pressure should not be taken during pregnancy. For example, medicines called angiotensin-converting enzyme (ACE) inhibitors, angiotensin-II receptor antagonists (AIIRAs) - sometimes called angiotensin receptor blockers (ARBs) - and water tablets. This is because these medicines may harm a developing baby. If you are taking one of these medicines then it is very likely that your medicine will be changed to another medicine that is not known to harm a developing baby.

Gestational high blood pressure

Some women can develop new high blood pressure during their pregnancy. This is called pregnancy-induced high blood pressure (or hypertension) or gestational high blood pressure (or hypertension).

Gestational high blood pressure is high blood pressure that develops for the first time after the 20th week of pregnancy. Doctors can confirm this type of high blood pressure if you do not go on to develop pre-eclampsia during your pregnancy (see below) and if your blood pressure has returned to normal within six weeks of giving birth. If you have gestational high blood pressure, you do not have protein in your urine when it is tested by your midwife or doctor during your pregnancy.

Note: some women may be found to have new high blood pressure after 20 weeks of pregnancy. At first, they may not have any protein in their urine on testing. However, they may later develop protein in their urine and so be diagnosed with pre-eclampsia (see below). You are only said to have pregnancy-induced hypertension if you do not go on to develop pre-eclampsia during your pregnancy.

Pre-eclampsia and eclampsia

Pre-eclampsia is a condition that can affect some women who develop new high blood pressure after the 20th week of their pregnancy. Pre-eclampsia can also sometimes develop in women who have high blood pressure before they are pregnant (pre-existing high blood pressure) or in women who have pre-existing protein in their urine (for example, due to pre-existing kidney problems).

Pre-eclampsia not only causes high blood pressure, but it also affects other parts of your body such as your kidneys, liver, brain and blood clotting system. Pre-eclampsia causes protein to leak from your kidneys into your urine. If you have pre-eclampsia, you will have high blood pressure and protein will be found in your urine when it is tested. Pre-eclampsia gets better within six weeks of you giving birth. See separate leaflet called Pre-eclampsia for more details.

Eclampsia can be a complication of pre-eclampsia. It is when a woman with pre-eclampsia has one or more seizures (fits, or convulsions). This is a serious condition. The aim is to detect and treat pre-eclampsia successfully to try to prevent eclampsia developing.

The reason why pregnancy may cause high blood pressure (hypertension) or pre-eclampsia is not fully understood. In women who develop pre-eclampsia, it seems to have something to do with a problem with the afterbirth (placenta). This is the attachment between your baby and your womb (uterus). It is thought that there are problems with the development of the blood vessels of the placenta in pre-eclampsia and also damage to the placenta in some way. This may affect the transfer of oxygen and nutrients to your baby. There are also certain women who seem to be at increased risk of developing pre-eclampsia.  The leaflet on pre-eclampsia gives more details.

High blood pressure (hypertension) during pregnancy is quite a common problem.

  • About 1 in 10 pregnant women have problems with high blood pressure.
  • About 1 in 20 pregnant women have pre-existing high blood pressure.
  • About 1 in 20 pregnant women have gestational high blood pressure and do not go on to develop pre-eclampsia.
  • Somewhere between 2 and 8 in 100 pregnant women develop pre-eclampsia.
  • Eclampsia develops in around 1 in 200 women with pre-eclampsia.

Problems with new high blood pressure are more common during your first pregnancy.

As a rule, the higher your blood pressure, the greater the risk for you and your baby.

Mild to moderate high blood pressure

If your blood pressure remains mildly to moderately raised and you do not develop pre-eclampsia, then the risk is low. Most women with high blood pressure (hypertension) during pregnancy just have mildly or moderately raised blood pressure. However, it is important that your blood pressure and urine should be checked regularly throughout your pregnancy and that you look out for any signs of possible pre-eclampsia (see below).

Severe high blood pressure or pre-eclampsia

Severe high blood pressure, especially with pre-eclampsia, is serious.

  • The risks to you as the mother include: an increased chance of having a stroke; damage to your kidneys and liver; an increased risk of blood clotting problems; an increased risk of severe bleeding from your placenta. Also, if you develop pre-eclampsia, there is a risk of eclampsia.
  • The risks to your baby include: an increased chance of poor growth; an increased chance of premature birth; an increased chance of stillbirth.

Many women with high blood pressure (hypertension) during their pregnancy do not have any symptoms. This is why your blood pressure is checked regularly by your doctor or midwife during your pregnancy. Your urine is also tested regularly for protein, to look for possible pre-eclampsia.

However, there are some symptoms that you should look out for that could be signs of pre-eclampsia. If you develop any of these, you should see your doctor or midwife urgently so that they can check your blood pressure and test your urine for protein. They include:

  • Severe headaches that do not go away.
  • Problems with your vision, such as blurred vision, flashing lights or spots in front of your eyes.
  • Tummy (abdominal) pain. The pain that occurs with pre-eclampsia tends to be mainly in the upper part of the abdomen, just below your ribs, especially on your right side.
  • Vomiting later in your pregnancy (not the morning sickness of early pregnancy).
  • Sudden swelling or puffiness of your hands, face or feet.
  • Not being able to feel your baby move as much.
  • Just not feeling right.

Note: swelling or puffiness of your feet, face, or hands (oedema) is common in normal pregnancy. Most women with this symptom do not have pre-eclampsia, but it can become worse in pre-eclampsia. Therefore, report any sudden worsening of swelling of the hands, face or feet promptly to your doctor or midwife.

If your doctor or midwife finds that your blood pressure is high during your pregnancy, they will usually check to see if you have any protein in your urine and ask you if you have any symptoms of pre-eclampsia. If your blood pressure remains high, or if you have any signs of pre-eclampsia, you will usually be seen by a specialist (an obstetrician). The specialist has to take into account such things as:

  • How severe is your high blood pressure (hypertension)?
  • Is there pre-eclampsia and, if so, how severe is it?
  • How far on is your pregnancy?
  • What are the risks to you, the mother, and your baby? This will depend on the severity of your high blood pressure and whether or not pre-eclampsia is present.

If high blood pressure remains mild and pre-eclampsia does not develop

There is usually little risk. Regular checks of your blood pressure and your urine for protein, as well as checks to see how your pregnancy is progressing, may be all that is needed until the natural time of birth. Checks may include blood tests and an ultrasound scan to look at how your baby is growing and to check the blood flow from the placenta to the baby. You may be followed up by a specialist (an obstetrician). You may need medicines to control your blood pressure during your pregnancy.

If high blood pressure becomes severe, or if pre-eclampsia develops

There are risks to both you, as the mother, and your baby if high blood pressure becomes more severe, especially if you develop pre-eclampsia. You will usually be seen urgently by a specialist and you may be admitted to hospital. Blood tests may be suggested to check to see how much your blood pressure or pre-eclampsia is affecting you. The well-being of your baby may also be checked using ultrasound scanning. A recording of your baby's heart rate may be carried out.

For severe high blood pressure, especially if pre-eclampsia develops, there is often a dilemma. If the high blood pressure is caused by the pregnancy, the only cure is to deliver your baby. This may be fine if your pregnancy is near to the end. The birth can be induced, or your baby can be born by Caesarean section if necessary.

However, a difficult decision may have to be made if high blood pressure or pre-eclampsia becomes severe earlier in your pregnancy. Medicine to lower the blood pressure may be prescribed for a while. This may allow your pregnancy to progress further before delivering your baby. The best time to induce the birth (or deliver by Caesarean section) varies depending on the factors mentioned above.

If you have severe pre-eclampsia, the medicine magnesium sulfate may be given via a drip around the time that your baby is delivered. This may reduce your chance of developing eclampsia.

There is some evidence to suggest that regular low-dose aspirin and calcium supplements may help to prevent pre-eclampsia in some women who may be at increased risk of developing it. Your specialist may recommend you take one or both of these. They will be able to discuss this with you in more detail.

Original Author:
Dr Tim Kenny
Current Version:
Peer Reviewer:
Dr John Cox
Document ID:
4485 (v39)
Last Checked:
20/12/2012
Next Review:
20/12/2015
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