If you're pregnant and have a history of high blood pressure (hypertension), or have developed high blood pressure for the first time in pregnancy, here's what you need to know about managing it.
What is high blood pressure
There are 3 levels of hypertension:
- mild – blood pressure between 140/90 and 149/99mmHg (millimetres of mercury); may be checked regularly but does not usually need treatment
- moderate – blood pressure between 150/100 and 159/109mmHg
- severe – blood pressure of 160/110mmHg or higher
If you're already taking medication for high blood pressure
If you're taking medicine to lower your blood pressure and want to try for a baby, talk to your GP or specialist first. They may want to switch you to a different medicine before you get pregnant.
If you find out you're already pregnant, tell your doctor immediately. They may need to change your medication 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.
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 that you don't develop a condition called pre-eclampsia. Make sure you go to all your antenatal appointments.
During the first half of pregnancy, a woman's blood pressure tends to fall. This means you may be able to come off your medication for a while. But this should only be done under your doctor's supervision.
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 balanced diet and keeping your salt intake low can help to reduce blood pressure.
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 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. 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.
Labour and birth
If you're taking medication throughout pregnancy to control your blood pressure, keep taking it 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 should be able to have a natural vaginal birth.
If you have severe hypertension, your blood pressure will be monitored continually in labour. Your doctors may also recommend your baby be delivered using forceps or ventouse, or by caesarean section.
After the birth, your blood pressure will be monitored.
If you had hypertension before you got pregnant, your treatment should be checked 2 weeks after your baby is born.
If you developed hypertension while you were pregnant and you're still taking medication 2 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 also be offered an appointment with a doctor at the postnatal check, around 6 weeks after the baby is born.
There isn't much information on whether blood pressure medicines pass into breast milk or if they may have any effect on a breastfed baby.
The drugs used to treat high blood pressure in pregnancy can usually be safely continued after the birth and while breastfeeding.
Talk to your midwife or doctor about breastfeeding if you're taking medication.