Blood pressure is a measure of the force of blood on artery walls (main blood vessels) as it flows through them.
It's measured in millimetres of mercury (mmHg) and recorded as 2 figures:
- systolic pressure – the pressure when the heart beats and squeezes blood out
- diastolic pressure – the pressure when the heart rests inbetween beats
Your GP or midwife will use a device with an inflatable cuff and a scale as a pressure gauge (a sphygmomanometer) to measure your blood pressure.
The systolic reading is taken first, followed by the diastolic reading.
If, for example, the systolic blood pressure is 120mmHg and the diastolic blood pressure is 80mmHg, the overall blood pressure will be 120 over 80, which is commonly written as 120/80.
High blood pressure during pregnancy is usually defined as a systolic reading of 140mmHg or more, or a diastolic reading of 90mmHg or more.
A urine sample is usually requested at every antenatal appointment. This can easily be tested for protein using a dipstick.
A dipstick is a strip of paper that's been treated with chemicals so it reacts to protein, usually by changing colour.
If the dipstick tests positive for protein, your GP or midwife may ask for another urine sample to send to a laboratory for further tests.
This could be a single sample of urine, or you may be asked to provide several samples over a 24-hour period.
These can be used to determine exactly how much protein is being lost through your urine.
If you're between 20 weeks and 34 weeks plus 6 days pregnant and your doctors think you may have pre-eclampsia, they may offer you a blood test to help rule out pre-eclampsia.
It measures levels of a protein called placental growth factor (PIGF). If your PIGF levels are high, it's highly likely that you don't have pre-eclampsia.
If your PIGF levels are low, it could be a sign of pre-eclampsia, but further tests would be needed to confirm the diagnosis.
Further tests in hospital
If you're diagnosed with pre-eclampsia, you should be referred to a specialist in hospital for further tests and more frequent monitoring.
Depending on the severity of your condition, you may be able to go home after an initial assessment and have frequent outpatient appointments.
In severe cases, you may need to stay in hospital for closer observation.
Read more about treating pre-eclampsia.