Your blood pressure (measured in millimetres of mercury, or mm Hg for short) is recorded regularly during your pregnancy. It is recorded as a higher (systolic) pressure and a lower (diastolic) pressure – for example, 120/70 mm Hg, or 120 over 70.
If you have high blood pressure, or hypertension, your heart has to work harder to pump the blood around your body. This can affect the heart muscle.
Hypertension affects around 10-15% of pregnancies. There are different types of hypertension in pregnancy, including:
- chronic hypertension (where the high blood pressure was present before pregnancy)
- pregnancy-related high blood pressure (gestational hypertension) and pre-eclampsia
For each of these different types of hypertension, there are three levels:
- mild hypertension refers to a blood pressure between 140/90 and 149/99 mm Hg – it may be checked regularly, but does not usually need treatment
- moderate hypertension refers to a blood pressure between 150/100 and 159/109 mm Hg
- severe hypertension refers to a blood pressure of 160/110 or higher
If you already have high blood pressure (chronic hypertension)
Many women with chronic hypertension will be taking drugs to keep their blood pressure within the range that is best for them (the target range). As blood pressure falls during the first half of pregnancy, it is sometimes possible to stop anti-hypertensive drugs, at least temporarily.
Some drug treatments for high blood pressure are not recommended in pregnancy. If you are taking tablets, it is important to see your doctor to find out whether you need to change to other drugs before you become pregnant. If you are taking medication to control your blood pressure and you become pregnant, tell your doctor immediately. You may need to change to a different medication – your doctor will talk to you about this.
If you take drugs to lower your blood pressure, this can reduce the blood flow to the placenta and to your baby. It is important that your antenatal team monitors you closely to ensure that the growth of your baby remains normal. Make sure you go to all your antenatal appointments with the midwife or doctor.
Find out what the placenta is.
While the type of treatment you are given will depend on the cause of your high blood pressure, the key to a healthy pregnancy is to make sure that your blood pressure remains under control. Having check-ups with your antenatal team is the best way of monitoring your condition. You should be offered additional antenatal appointments based on your needs and the needs of your baby.
You should keep active and get some physical activity each day, such as walking or swimming. Read more about exercise in pregnancy. Eat a healthy, balanced diet and keep your salt intake low, as this can reduce blood pressure.
Find out about healthy eating in pregnancy, salt in the diet and tips for cutting down on salt.
You may have heard that some supplements, such as garlic, might prevent high blood pressure. The truth is that there isn't enough evidence to show that the following supplements are effective, and they are not recommended as a means of preventing high blood pressure in pregnancy:
- folic acid
- antioxidants (vitamins C and E)
- fish or algal oils
High blood pressure as a result of pregnancy
Pregnancy-induced hypertension, or gestational hypertension, affects around 16% of pregnancies. This means that out of 100 pregnant women, 16 will develop high blood pressure in pregnancy. This usually occurs late in pregnancy (after 32 weeks).
Find out about pregnancy-induced hypertension and pre-eclampsia.
Pre-eclampsia is a pregnancy-related condition that usually causes high blood pressure and protein in the urine (proteinuria). It is more common if you have high blood pressure before becoming pregnant, or if you have had pre-eclampsia in a previous pregnancy. If this applies to you, attending regular check-ups to have your blood pressure and urine tested is even more important.
Pre-eclampsia also affects the placenta, so regular scans are needed to check that your baby grows normally and remains healthy. Pre-eclampsia affects 2-5% of pregnancies. If untreated, it can lead to seizures (fits) and, on rare occasions, the mother's death.
healthtalk.org has videos of women talking about their experiences of having other conditions in pregnancy, including pre-eclampsia.
Read about what happens in labour and your options for pain relief.
Labour and birth
If you are taking medication to control your blood pressure, keep taking this during labour.
If you have mild or moderate hypertension, your blood pressure should be monitored hourly during labour. As long as your blood pressure remains within target levels, you can hope for a natural vaginal birth.
If you have severe hypertension, your blood pressure will be monitored continually in labour. If your high blood pressure is severe, you may be recommended an operative delivery (forceps or ventouse) or caesarean section.
After the birth, your blood pressure will be monitored. If you have chronic hypertension, your treatment should be checked two weeks after your baby is born.
If you developed gestational hypertension and you're still taking medication two weeks after the birth, you should be offered an appointment with a doctor to check whether your treatment needs to be changed or stopped.
All women with hypertension in pregnancy should be offered an appointment with a doctor at the postnatal check, around six weeks after the baby is born.
For most anti-hypertensive drugs, there is limited information on whether they pass into breast milk or whether they may have any effect on a breastfed baby. Talk to your midwife or doctor about breastfeeding if you're taking medication.
The National Institute for Health and Care Excellence (NICE) produces guidance on the management of hypertension in pregnancy.