High blood pressure in pregnancy

Also known as hypertension in pregnancy

Blood pressure is a measure of the pressure in the large vessels (arteries) leading from your heart to your other organs. In pregnancy, this includes your uterus (womb) and placenta where your baby is growing.

Key points

  1. You may have high blood pressure before you became pregnant, develop it during pregnancy or develop a serious related condition, pre-eclampsia.
  2. High blood pressure usually doesn’t cause symptoms until it's very high, so you need to get it checked at each antenatal visit, as well as your urine protein levels.
  3. The main risk of having high blood pressure in pregnancy is developing pre-eclampsia. If you develop pre-eclampsia, there are risks to you and your baby.
  4. If your blood pressure remains mildly to moderately raised and you don't develop pre-eclampsia, the risk of pregnancy complications is low.

If you have any of the following symptoms contact your midwife or lead maternity carer (LMC) straight away. These could be warning signs of pre-eclampsia:

  • ongoing, persistent or severe headache
  • changes in eyesight such as seeing spots, flashing lights or floaters, blurry vision
  • pain in your upper belly, tummy area or shoulder
  • sudden and new swelling in your face, hands or eyes (some feet and ankle swelling is normal during pregnancy)
  • sudden weight gain (more than 1 kg in a week or more than 3 kg in a month)
  • vomiting later in your pregnancy (not the morning sickness of early pregnancy)
  • difficulty breathing.

What are the causes of high blood pressure in pregnancy?

The causes of high blood pressure in pregnancy depend on what type of high blood pressure you have.

If you have pre-existing hypertension or chronic hypertension, it is usually due to family history. Sometimes kidney or glandular disease may be responsible. However, eating too much salt, drinking too much alcohol, being overweight and not moving around enough each day can also contribute to high blood pressure.

If you have pregnancy-induced hypertension or pre-eclampsia, it is due to abnormal development of the placenta in your womb.

A baby receives all its food and oxygen from the mother. This means that your heart has to work harder to send blood to the placenta and then to your baby.

The placenta usually has large blood vessels which make it easy for the food to get to your baby. Because these blood vessels are so big, your blood pressure normally drops during the middle third of your pregnancy and returns to normal by the end of the pregnancy. 

If your blood pressure is too high during pregnancy, this may indicate that the blood vessels in the placenta have not developed normally. This is a risk to you and your baby, as it can be a sign of a serious complication known as pre-eclampsia.

How is blood pressure measured?

Blood pressure is shown as 2 numbers:

  • The top number (systolic) is the highest pressure in your arteries when your heart pumps blood to the rest of your body.
  • The bottom number (diastolic) is the lowest pressure when your heart rests between heartbeats.

Blood pressure is normally written as the top number over the bottom number, such as 120/80.

High blood pressure may be considered to be 140/90 mmHg or higher. However, it is difficult to give an example of a high blood pressure reading, because it depends on the individual. The level of blood pressure that is high for you depends on lots of different factors and your overall risk of heart attack or stroke.

Generally, the lower your blood pressure, the better. If you have a history of heart disease, diabetes or a high risk of heart attack or stroke, it's recommended you lower your blood pressure to less than 130/80. See who needs to get their blood pressure checked?

What are the different types of high blood pressure in pregnancy?

There are 3 types of high blood pressure (hypertension) in pregnancy.

  1. Pre-existing hypertension or chronic hypertension – this is when you already have high blood pressure before pregnancy or in the first 20 weeks. High blood pressure before 20 weeks of pregnancy is not caused by pregnancy because the placenta is not fully developed. Read more about pre-existing hypertension or chronic hypertension.
  2. Pregnancy-induced hypertension or gestational hypertension – this is high blood pressure that you develop after 20 weeks of pregnancy. Some women just develop high blood pressure and no other problems, but some develop a condition called pre-eclampsia, where other organs in your body are affected. 
  3. Pre-eclampsia – this is a serious condition that only happens in pregnant women and develops after 20 weeks. The main feature is high blood pressure, but for a diagnosis of pre-eclampsia there must also be evidence that other organs are affected, such as protein in your urine. Your kidneys, liver, brain, placenta and blood clotting system are the organs most commonly involved. Women with pre-existing hypertension can also develop pre-eclampsia. Once you develop pre-eclampsia, you need to be watched closely, as pre-eclampsia doesn’t go away until your baby is born and it can lead to eclampsia (a complication of pre-eclampsia). Read more about pre-eclampsia.

How is high blood pressure in pregnancy diagnosed?

High blood pressure usually doesn’t cause symptoms until your blood pressure is very high, so it is usually found during an antenatal visit when you have your blood pressure checked.

At each antenatal visit, your midwife or LMC will check your blood pressure and test your urine for protein. An increase in these are warning signs of pre-eclampsia.

High blood pressure in pregnancy can be diagnosed if your blood pressure is consistently high on 2 occasions. A sudden increase in blood pressure is often the first sign of a problem. Your midwife will also check if you have any of the symptoms listed above.

Why is high blood pressure during pregnancy a problem?

The main risk of having high blood pressure during pregnancy is developing pre-eclampsia. Pre-eclampsia is a serious condition and it can affect both you and your baby. Read more about pre-eclampsia.

If your blood pressure remains mildly to moderately raised and you don’t develop pre-eclampsia, the risk of pregnancy complications is low. However, it is important that your blood pressure and urine are checked regularly throughout your pregnancy to check for signs of pre-eclampsia.

How is high blood pressure during pregnancy treated?

The type of treatment will depend on how bad your blood pressure is and whether you have developed pre-eclampsia. You may need to be referred to an obstetrician if you have severe high blood pressure and are at risk of developing pre-eclampsia.

If you only have high blood pressure and not pre-eclampsia, your blood pressure can usually be controlled by diet and lifestyle changes or antihypertensive medications and you can have a normal pregnancy. You will be taught the signs and symptoms of pre-eclampsia to watch out for as you must contact your midwife or doctor if these symptoms develop.

If pre-eclampsia does develop, you will need much closer supervision and will probably need to have your baby early. The treatment and monitoring is aimed to keep you and your baby safe while your baby grows and develops as much as possible. If your baby does need to be delivered early there are treatments available to decrease the complications of being born prematurely. Read more about treatment and monitoring for pre-eclampsia.

Some of the medications that may be prescribed to you include:

  • antihypertensives such as labetalol, nifedipine or methyldopa
  • low-dose aspirin from 12 weeks of pregnancy
  • calcium
  • magnesium sulphate to prevent seizures.

Self-care – what can you do to look after yourself with high blood pressure in pregnancy?

Take the following steps to help control your blood pressure and have a healthy pregnancy:

  • Attend all your antenatal check-ups so your doctor or midwife can check your blood pressure and urine protein levels. 
  • Know the signs and symptoms of pre-eclampsia and contact your midwife or LMC straight away if you have these.
  • Don't smoke. This is one of the best things you can do to lower your blood pressure and help your baby be healthy. If you need help to quit smoking, talk to your doctor.
  • Gain an amount of weight that is healthy for you. Your doctor or midwife can help you set a pregnancy weight goal.
  • Get regular gentle exercise during pregnancy. Walking or swimming several times a week can help lower blood pressure which is good for you and your baby. 
  • Try to keep your stress level low. This may be hard to do, especially if you continue to work, have young children or have a hectic schedule. But try to find some time to relax.

Learn more

Diabetes and high blood pressure National Women’s Health, ADHB, NZ
High blood pressure in pregnancy Patient Info, UK
High blood pressure in pregnancy National Institute for Health and Care Excellence (NICE), UK

References

  1. Hypertension in pregnancy and postpartum Auckland Regional HealthPathways, NZ
  2. The SOMANZ guideline for the management of hypertensive disorders of pregnancy Society of Obstetric Medicine of Australia and New Zealand (SOMANZ),  2014
  3. Hypertension in pregnancy National Institute for Health and Care Excellence (NICE), UK, 2013 
Credits: Health Navigator Editorial Team. Reviewed By: Dr Jeremy Tuohy, University of Auckland Last reviewed: 07 Oct 2016