High blood pressure, or hypertension, does not usually make you feel unwell, but it can sometimes be serious in pregnancy.
Your midwife will check your blood pressure at all your antenatal (pregnancy) appointments.
If you are pregnant and have a history of high blood pressure (chronic hypertension), you should be referred to a specialist in hypertension and pregnancy to discuss the risks and benefits of treatment.
If you are found to have high blood pressure in pregnancy (gestational hypertension), you will be assessed in a hospital by a healthcare professional, usually a midwife.
What is high blood pressure
Hypertension in pregnancy is defined as having a blood pressure reading between 140/90 and 159/109mmHg (millimetres of mercury). This means your blood pressure may need to be checked regularly but you do not always need treatment.
Severe hypertension in pregnancy is defined as having a blood pressure reading of 160/110mmHg or higher. This will require treatment until the reading is below 160/110mmHg.
If you are already taking medicine for high blood pressure
If you're already taking medicine to lower your blood pressure and want to try for a baby, talk to your GP or specialist first. They may want you to switch to a different medicine before you get pregnant.
If you find out you're already pregnant, tell your doctor immediately. You may need to change your medicine as soon as possible.
This is because some medicines that treat high blood pressure may not be safe to take when you're pregnant. They can reduce the blood flow to the placenta and your baby, or affect your baby in other ways.
Your pregnancy appointments
It's important that your antenatal team monitors you closely throughout your pregnancy to make sure your high blood pressure is not affecting the growth of your baby and to check for a condition called pre-eclampsia. Make sure you go to all your appointments.
Your doctor or midwife will measure your blood pressure and check for protein in your urine at every appointment. After 20 weeks of pregnancy, you may be offered a PLGF (placental growth factor) blood test to rule out pre-eclampsia.
During the first half of pregnancy, your blood pressure tends to fall. This means you may be able to come off your medicine for a while. But this should only be done after discussion with your doctor.
Things you can try yourself to reduce high blood pressure
Keeping active and doing some physical activity each day, such as walking or swimming, can help keep your blood pressure in the normal range. Eating a healthy, balanced diet can help to reduce blood pressure.
Find out about exercise in pregnancy and healthy eating in pregnancy.
There isn't enough evidence to show that dietary supplements – such as magnesium, folic acid or fish oils – are effective at preventing high blood pressure.
Pre-eclampsia
Pre-eclampsia is a condition that affects some pregnant women, typically after 20 weeks.
It is a problem with the placenta that usually causes your blood pressure to rise and can affect organs such as the kidney, liver and brain. If left untreated, pre-eclampsia can be dangerous for you and your baby.
Pre-eclampsia is more common if you had high blood pressure before becoming pregnant, if you had pre-eclampsia in a previous pregnancy, or if you have a family history of your mother or sister developing pre-eclampsia.
You can feel well if you have high blood pressure, so it is important to attend your regular check-ups to have your blood pressure and urine tested. Read more about pre-eclampsia and how pre-eclampsia is treated.
Labour and birth
If you have hypertension in pregnancy your doctor might want to discuss how this could affect your birth plan, including the timing of birth.
If you're taking medicine throughout pregnancy to control your blood pressure, keep taking it during labour.
If you have hypertension, your blood pressure should be monitored hourly during labour. As long as your blood pressure remains within target levels, it should not stop you from being able to have a vaginal birth.
If you have severe hypertension, your blood pressure will be monitored every 15 to 30 minutes in labour. Your doctors may also recommend you give birth using forceps or ventouse, or by caesarean section.
After the birth, your blood pressure will be monitored.
Check-ups after the birth
If you had hypertension before you got pregnant or developed hypertension while you were pregnant and you're still taking medicine after the birth, you should be offered an appointment with a doctor 2 weeks after you transfer from hospital care to community midwives, or 2 weeks after the birth if you had a home birth.
This is to check whether your treatment needs to be changed or stopped.
Everyone with hypertension in pregnancy should also be offered an appointment with a GP or specialist 6 to 8 weeks after their baby is born.
This appointment is to check your blood pressure, in addition to your routine 6-week postnatal check.
Breastfeeding
Talk to your midwife or doctor about breastfeeding if you're taking medicine.
You should be able to breastfeed if you need to take hypertension medicine. Your treatment can be changed if needed, in a discussion with your doctor.
Hypertension medicines can pass into breast milk. Most lead to very low levels in breast milk, and the amount taken in by babies is very small.
Most medicines are not tested during pregnancy or breastfeeding. Disclaimers or warnings in the manufacturer's information are not because of specific safety concerns or evidence of harm.
Find out about specific medicines and pregnancy on the Bumps (Best use of medicines in pregnancy) website.