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
You may have high blood pressure before you became pregnant, develop it during pregnancy or develop a serious related condition, pre-eclampsia.
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.
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.
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 normal blood pressure changes in pregnancy?
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 that 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.
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.
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.
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.
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.
Dr Jeremy Tuohy is an Obstetrician and Gynaecologist with a special interest in Maternal and Fetal Medicine. Jeremy has been a lecturer at the University of Otago, Clinical leader of Ultrasound and Maternal and Fetal Medicine at Capital and Coast DHB, and has practiced as a private obstetrician. He is currently completing his PhD in Obstetric Medicine at the Liggins Institute, University of Auckland.
Credits: Health Navigator Editorial Team. Reviewed By: Dr Jeremy Tuohy, The University of Auckland
Last reviewed: 05 Aug 2020
What is pre-existing hypertension or chronic hypertension?
You may have high blood pressure (hypertension) that started before your pregnancy, or high blood pressure that is diagnosed before 20 weeks of pregnancy. In this case, the high blood pressure is not caused by pregnancy and is called pre-existing hypertension or chronic high blood pressure.
Up to 1 in 20 women have pre-existing high blood pressure when they become pregnant.
Pre-existing high blood pressure usually doesn't go away even after your baby is born.
Women with pre-existing hypertension have a higher chance (20%) of developing pre-eclampsia.
If you have pre-existing hypertension and are on antihypertensive medications, you need to let your GP or midwife know once you are pregnant or if you are planning for a pregnancy. Some of the usual antihypertensive medications may not be safe to use in pregnancy.
What causes pre-existing hypertension or chronic hypertension?
High blood pressure often runs in families. 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 and heart disease.
The effects of high blood pressure on your blood vessels are worsened by:
What are the complications of pre-existing hypertension in pregnancy?
The main complication of having pre-existing hypertension in pregnancy is developing pre-eclampsia. Women with pre-existing hypertension have a higher chance (20%) of developing pre-eclampsia. This is why women with pre-existing hypertension need to be monitored closely during pregnancy.
placental abruption (severe bleeding from your placenta).
How is pre-existing hypertension in pregnancy diagnosed?
If you have pre-existing hypertension, you will usually be diagnosed before pregnancy or be on antihypertensive medications.
However, because high blood pressure doesn’t usually cause any symptoms, it may not be diagnosed until an antenatal visit (before 20 weeks) when you have your blood pressure checked. High blood pressure in pregnancy can be diagnosed if your blood pressure is consistently high in 2 occasions.
At each antenatal visit, your midwife or LMC will check your blood pressure and test your urine for protein. Your midwife will also check if you have any of the following symptoms:
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.
An increase in these are warning signs of pre-eclampsia. A sudden increase in blood pressure is often the first sign of a problem.
How is pre-existing hypertension in pregnancy treated?
Women with pre-existing hypertension need to be closely monitored throughout the pregnancy. You will be taught the signs and symptoms of pre-eclampsia to watch out for as it is important to contact your midwife or GP if you develop any of these symptoms.
Treatment depends on how bad your blood pressure is and whether you have developed pre-eclampsia.
If you are taking medicines to treat high blood pressure before pregnancy and you are planning a pregnancy, speak to your doctor, nurse or midwife about reviewing your medication before you become pregnant. Your medication will be changed to one that is considered safe in pregnancy.
If you are taking medicines to treat high blood pressure and you have just found out that you are pregnant, contact your doctor immediately so that your medication can be reviewed.
Commonly prescribed antihypertensives in pregnancy
Commonly used blood pressure medicines (antihypertensives) during pregnancy include:
When deciding whether or not to take antihypertensives during pregnancy, your doctor will discuss with you how necessary the medication is to your health against the possible risks to you or your baby, some of which will depend on how many weeks pregnant you are.
Additional medications
Because women with pre-existing hypertension have a higher chance of developing pre-eclampsia and other complications during pregnancy, you may also be given medicines to help prevent pre-eclampsia, such as:
Examples include bendroflumethiazide, chlortalidone, indapamide, furosemide, hydrochlorothiazide, amiloride.
Severe hypertension or if pre-eclampsia develops
If your blood pressure becomes severely high or you develop pre-eclampsia, you may be referred to an obstetrician or a specialist for treatment or monitoring and may need admission to hospital. You will need much closer supervision and will probably need to have your baby early.
The treatment and monitoring aim 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.
Severe hypertension – systolic pressure ≥ 160 mmHg or diastolic pressure ≥ 110 mmHg.
About hypertension in pregnancy and postpartum
Defined as a systolic blood pressure (SBP) ≥ 140 mmHg or diastolic blood pressure (DBP) ≥ 90 mmHg, as measured on 2 or more consecutive occasions at least 4 hours apart.
Classifications
Eclampsia – new onset of seizures in association with pre-eclampsia.
Pre-eclampsia – new onset of hypertension after 20 weeks' gestation or superimposed on pre-existing hypertension and one or more of the following develop as new conditions: • Proteinuria – protein:creatinine ratio ≥ 30 mg/mmol or 2+ on dipstick confirmed by protein:creatinine ratio test. • Other maternal organ dysfunction: ◊ Renal insufficiency ◊ Elevated ALT and AST ◊ Neurological complications eg, hyperreflexia with clonus, severe headaches, persistent visual scotomata, altered mental status, blindness, stroke. ◊ Haematological complications (platelets < 100 x 109/L, haemolysis) • Uteroplacental dysfunction eg, fetal growth restriction, abruption.
HELLP syndrome (haemolysis, elevated liver enzymes, low platelet count) – is a variant of pre-eclampsia but does not require hypertension for a diagnosis.
Women who have had pre-eclampsia are at increased risk of cardiovascular disease in later life.
Chronic or pre-existing hypertension – Chronic or pre-existing hypertension is hypertension that is confirmed before conception or before 20 weeks' gestation, with or without known cause, as measured on 2 or more consecutive occasions at least 4 hours apart. • These women have a higher risk (20%) of pre-eclampsia. • Associated increase risk of pre-term birth, fetal growth restriction, placental abruption. • The main benefit of anti-hypertensive treatment is in decreasing maternal mortality from severe hypertension such as stroke, heart failure and renal failure.
Gestational hypertension – New onset hypertension (≥ 140/90) after 20 weeks' gestation in a patient who had normal blood pressure before 20 weeks' gestation, in the absence of abnormalities that define pre-eclampsia, and the blood pressure returns to normal within 3 months after giving birth. • Requires close monitoring.
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