Antenatal hypertension (high blood pressure in pregnancy)

Antenatal hypertension is the medical term for high blood pressure during pregnancy. If you have hypertension, or are at risk of it, we offer specialist care to help look after you and your baby during your pregnancy.

About 1 in 10 women have high blood pressure during pregnancy.

If hypertension is not managed, your blood pressure can increase. Very high blood pressure means you are more likely to have complications such as pre-eclampsia.

We treat high blood pressure with medicine and will monitor you at the clinic, but you might also want to check your blood pressure and urine (pee) at home, between appointments. We will help you to do this, and understand when you need to seek medical help.

Hypertension might also affect your labour, but we will talk to you about the different options and help you to plan.

The hypertension in pregnancy clinic

You have been asked to come to the hypertension in pregnancy clinic because:

  • you already have high blood pressure
  • you were diagnosed with high blood pressure early in pregnancy
  • you have a medical condition that means you are more likely to get high blood pressure
  • you have protein in your urine or other kidney problems in this pregnancy

Our team of doctors and specialist midwives at the clinic are here to help you manage your hypertension. At your appointments we will:

  • ask you how you are feeling
  • check on your baby’s well-being
  • measure your blood pressure
  • measure the protein in your urine
  • occasionally take blood tests to check how your kidneys, liver and blood are working

These tests help us to check that you and your baby are safe. We may recommend you have other tests or treatment.

At the clinic we will get to know your individual needs. We will work with you to plan your care and any treatment you may need to keep you and your baby safe.

We make regular appointments to see you at the hypertension in pregnancy clinic. If your doctor or midwife tells you your blood pressure is too high, or you have checked it at home and it is high, we will want to see you sooner than your next booked appointment.

Causes of high blood pressure

There are lots of things that can affect your blood pressure, including being anxious or stressed, such as when having to rush. Some people find it stressful being in hospital. Other factors may contribute to blood pressure, such as a family history of blood pressure problems, and being overweight or smoking.

Your body has lots of ways of keeping blood pressure within the normal range so, if your blood pressure is high, it is important that you take medicines to keep you healthy. Most women do not have any symptoms when their blood pressure is high.

Hypertension before pregnancy (chronic)

If you are diagnosed with high blood pressure before you become pregnant, or within the first 20 weeks of your pregnancy, you have chronic or ‘pre-existing’ hypertension. This is not caused by your pregnancy and usually will not go away once you have given birth.

If you have chronic hypertension you are likely to be taking medicines already. It's important that you come to the hypertension in pregnancy clinic early in your pregnancy so we can check you are getting the right treatment and that it is safe for your baby.

How hypertension can affect pregnancy

Having high blood pressure in pregnancy means your blood pressure is more likely to become very high. This chance can be lowered by taking blood pressure medicines.

High blood pressure in pregnancy can be serious. Women with severely high blood pressure, and their babies, are more likely to have complications, than women with high or normal blood pressure. Complications may include:

  • developing pre-eclampsia
  • slowed growth of your baby
  • the need for early delivery
  • baby admission to the neonatal unit after birth

Women with severe high blood pressure or pre-eclampsia are also at a higher risk of serious complications, such as:

  • having a stroke
  • having severe bleeding from behind the placenta before your baby is born, known as a placental abruption


High blood pressure in pregnancy increases the risk of developing pre-eclampsia.

Pre-eclampsia is an illness you can get only during your pregnancy or straight after your baby is born. Changes in blood vessels all over your body may result in

  • your blood pressure rising and protein leaking into the urine
  • slowed growth of your baby
  • effects on your kidneys, liver, blood clotting or nervous system

Pre-eclampsia is detected by regular blood pressure measurements, urine samples, blood tests and regular growth scans of your baby. It can be more difficult to diagnose in women who already have high blood pressure or protein in their urine.

This is why it is important to attend all your antenatal appointments, where these tests will be done.

By being aware of the signs, you can help us to diagnose you quickly if you do develop pre-eclampsia.

Call your midwife, GP or NHS 111 immediately if:

  • you have any headache, especially if it is severe or pounding
  • you notice severe swelling in your hands, feet or face, especially around the eyes
  • you notice changes to your vision, such as blurriness, loss of sight, double vision or flashing lights
  • you have severe pain or tenderness under the ribs
  • you feel sick (nausea) or are being sick (vomiting) other than usual morning sickness

Treating high blood pressure in pregnancy

If your blood pressure is high, we usually offer you tablets to treat it, and to try to stop severely high blood pressure from happening.

The most common medicines that are nationally recommended for use in pregnancy are labetalol, nifedipine, and methyldopa. This is because they have been used for a long time and are safe to use in pregnancy. These are known as ‘anti-hypertensives’. We will recommend the medicine we think is most likely to work for you.

All 3 medicines can commonly cause dizziness and tiredness (about 1 in 10 people). If you have headaches as a side effect, this usually gets better after 2 days of taking the medicine.

If one medicine doesn’t work so well, another one can be tried, or a combination of 2 or 3 together.

We may also recommend you take a low-dose aspirin (75mg or 150mg) tablet from 12 weeks of pregnancy and may suggest vitamin D and folic acid.


This medicine should not be used if you have asthma. Please tell your doctor and midwife if you have asthma.

Common side effects are headaches and shortness of breath. Labetalol may also cause low blood sugars in babies immediately after birth, and tests will be done to check this. If the baby has low blood sugar, feeding with more milk or small amounts of sugar solution will usually raise their blood sugar level.


A common side effect is headaches. You can take painkillers such as paracetamol to help with headaches.


This is not used as often as a first choice as it can cause drowsiness and occasionally makes women feel depressed.

How to check your blood pressure at home

If you are at high risk of pre-eclampsia or have early signs of the illness, it can be reassuring to check your blood pressure and urine at home between antenatal appointments. The doctors and specialist midwives in the hypertension in pregnancy clinic can support you with this.

Your blood pressure (BP) is written as 2 numbers, for example, 120/60mmHg.

  • The first and higher number (in this example, 120) is the systolic pressure. This is the pressure on your arteries (blood vessels) when your heart contracts or beats.
  • The lower number (in this example, 60) is the diastolic pressure. This is the pressure on your arteries when your heart relaxes between beats.

The mmHg is how we measure blood pressure and means millimetres of mercury.

If you are not already taking medical treatment for blood pressure, tell your midwife or doctor if you have multiple readings of 140/90mmHg or higher over time as you might need more tests.

If you are taking medicine for high blood pressure, we aim for a blood pressure reading between 110/70mmHg and 135/85mmHg.

Only one of the numbers (systolic or diastolic) needs to be high, not both, for blood pressure to be considered high.

If your blood pressure is over 150/100

If your blood pressure is over 150/100 we want to see you that same week. Call the hypertension in pregnancy clinic and ask for an appointment slot, available on Wednesday afternoons.

If your blood pressure is over 160/110

Go to the maternity assessment unit (MAU) the same day if:

  • the top blood pressure number (systolic) is over 160


  • if you feel unwell

The maternity assessment unit is open 24 hours a day, 7 days a week. Please call the MAU to let us know you are coming.

Severely high blood pressure is 160/110mmHg or higher.

Planning the birth of your baby

As your pregnancy progresses we will talk to you about your preferences for the birth of your baby.

If you need medicine for high blood pressure during labour, we will recommend continuous electronic fetal monitoring. This is because having hypertension makes it more likely that your baby will become distressed in labour.

We monitor the baby using a cardiotocograph (CTG) held to your tummy with an elastic strap. This tells us how well your baby is coping during labour, and it will also alert us to any sudden changes, such as a placental abruption. We will talk to you about this and make an individual care plan for you and your baby.

We commonly suggest that women with uncomplicated hypertension are delivered by 40 weeks (their due date).

Inducing labour if your blood pressure rises

We may bring this forward if your blood pressure rises during the pregnancy or we have other concerns (such as your baby not growing as well as we would like).

Most often this involves induction of labour with the use of a pessary which contains a hormone medicine. It is placed in your vagina, close to the neck of your womb (cervix). The medicine softens the cervix and may also lead to the start of regular contractions.

If there are concerns about how you or your baby will cope with labour, we may suggest that you have a caesarean section.

You can discuss the options available to you with one the clinic doctors or the specialist midwife.

Information and support

This section explains where you can find more information and support.

Action on Pre-eclampsia

This is a charity for people affected by pre-eclampsia.

Helpline: 01386 761 848, Monday to Thursday, 8.30am to 4pm

Website: action-on-pre-eclampsia.org.uk

NHS website

NHS.uk has information on healthy eating and exercise after childbirth.

Resource number: 4284/VER3
Last reviewed: January 2024
Next review due: January 2027

A list of sources is available on request.

Contact us

The hypertension in pregnancy clinic is on Wednesday afternoons between 2 and 5pm.

Address: Antenatal Clinic, Floor 8, North Wing, St Thomas’ Hospital.

Phone: 020 7188 8001

Medical help

If you are concerned about your blood pressure or feel unwell, it is important to seek professional advice as soon as possible, even if it is late at night.

Call the maternity assessment unit (MAU) phone 020 7188 1723

Address: Floor 7, North Wing, St Thomas’ Hospital, Westminster Bridge Road, London SE1 7EH

We are open 24 hours a day, 7 days a week, including bank holidays.

Pregnancy advice and blood test results

For general pregnancy advice or blood test results you can call the maternity helpline

Phone: 020 7188 1723 Monday to Friday, 10am to 6pm, except bank holidays

Do you have any comments or concerns about your care?

Contact our Patient Advice and Liaison Service (PALS)

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