Blood pressure in pregnancy

Your midwife will check your blood pressure at every antenatal appointment. Making sure your blood pressure is at a healthy level is an important part of looking after you and your baby during pregnancy.

How will my blood pressure change in pregnancy?

It’s perfectly normal for your blood pressure to change a little during pregnancy (Bramham et al 2013, Foley 2019). The hormone progesterone relaxes the walls of your blood vessels. This may make your blood pressure fall during your first trimester and second trimester (Bramham et al 2013, Stöppler 2016, Foley 2019). You may find you feel faint if you stand for too long or get up quickly (Marks 2019, Stöppler 2016).

Your blood pressure is at its lowest in mid-pregnancy and starts to rise gradually again in your last trimester (Bramshaw et al 2013, Marks 2019). By this time, you’ll have made at least an extra litre (1.8 pints) of blood, which your heart has to pump around your body (Bauer 2019, de Haas et al 2017).

Your blood pressure may return to its pre-pregnancy levels in the last few weeks before your baby is born (Bramham et al 2013, Foley 2019).

How is my blood pressure measured?

Your midwife will use a small monitor to measure and record your blood pressure at every antenatal check-up (NICE 2019a).

Before your midwife measures your blood pressure, she’ll ask you to sit down and remove any tight clothing from your arm. Then she’ll wrap a cuff around your arm above your elbow and pump air into it.

The cuff inflates and briefly stops the blood flow in the main blood vessel in your arm. It will feel tight, but it shouldn’t hurt. Then the air in the cuff is slowly released. The cuff is attached to the monitor, which calculates your blood pressure and shows a reading to your midwife.

The reading will show two figures that look like a fraction: for example, 110/70. The first, or top, number tells your midwife about your blood pressure as your heart pushes the blood round your body (systolic blood pressure). The second, or bottom, number is your blood pressure when your heart relaxes between beats (diastolic).

What’s normal for you could be different from other mums-to-be, so it’s best not to compare results. The average blood pressure range, if you’re healthy, is between 90/60 and 120/80 (NHS 2019), although this varies a lot in pregnancy (Bramham et al 2013, Foley 2019).

Your midwife will tell you if your numbers are high. She’ll diagnose high blood pressure if your top figure (systolic) is 140 or higher, or your bottom figure (diastolic) is 90 or more (NICE 2019b).

There are two grades of high blood pressure (hypertension) in pregnancy:

• Hypertension is when your top figure is between 140 and 159 and your bottom figure is between 90 and 109
• Severe hypertension is when your top figure is 160 or greater and your bottom figure is 110 or greater
  (NICE 2019b)

During an antenatal appointment, if your midwife discovers you have high blood pressure, she’ll ask you to come back and have it checked again or go to your local maternity unit for monitoring. If it’s severe, you may be admitted to hospital until it falls (NICE 2019b).

High blood pressure has different names, depending on what stage in your pregnancy you develop it:

• Before you’re 20 weeks pregnant, if you have high blood pressure, it’s called chronic hypertension or pre-existing high blood pressure. This means you probably had high blood pressure before you became pregnant. You’ll only know for sure if this is the case if your blood pressure stays high after your baby is born.
• After 20 weeks, high blood pressure is called gestational hypertension. This is the name for high blood pressure that develops only during pregnancy.
  (NICE 2019b)

Gestational hypertension isn’t usually a problem, although you may be referred to a hospital outpatients clinic for more testing and monitoring, just in case (NICE 2019b).

Why is my blood pressure measured?

Measuring your blood pressure is a way of telling how well your pregnancy is going. Your midwife will be watching for signs of a potentially serious condition called pre-eclampsia, particularly later on in your pregnancy (NHS 2018a, NICE 2019a).

Pre-eclampsia is thought to happen when the placenta isn’t working as well as it should (August and Sibai 2019, NHS 2018b). This can lead to high blood pressure and other problems. Your midwife will test your urine as well as take your blood pressure at every antenatal appointment (NICE 2019a). Protein in your urine and high blood pressure are both signs of pre-eclampsia (August and Sibai 2019, NHS 2018b, NICE 2019b).

Having either pre-existing hypertension or gestational hypertension means you’re more likely to develop pre-eclampsia (August and Sibai 2019, NHS 2018b, NICE 2019b). Your risk rises further if you develop gestational hypertension before 35 weeks of pregnancy (NICE 2019c). However, this doesn’t mean you’ll definitely get it, and your doctor or midwife will make sure that you’re monitored more carefully throughout your pregnancy (NICE 2019b).

You may develop gestational hypertension and pre-eclampsia without realising it. In fact, you may feel perfectly well. That’s why it’s important to go to all your antenatal appointments so your midwife can regularly check your blood pressure and urine.

Knowing the symptoms of pre-eclampsia will help. If you feel unwell for no obvious reason between antenatal appointments, contact your midwife or doctor. Occasionally, pre-eclampsia can develop quickly and it’s important to get medical help straight away (NHS 2018b, NICE 2019b).

Will my blood pressure go down after the birth?

Blood pressure usually falls immediately after you’ve given birth (Foley 2019). Then it rises again, peaking three days to six days later (August 2020, Bramham et al 2013). That’s the case for women who had normal blood pressure during pregnancy, as well as those with high blood pressure (August 2020, Bramham et al 2013).

It’s quite normal for your blood pressure to fluctuate a bit in the weeks after the birth. It will probably be back to normal within a few weeks of having your baby (August 2020, Folk 2018).

Your blood pressure will be checked at least once within six hours of your baby’s birth (NICE 2006). After that, if you had gestational hypertension or chronic hypertension, your midwife will check it daily for the first two days, then once between days three and five after the birth (NICE 2019b).

If you had gestational hypertension and your blood pressure stays high, you may need to take medication to control it for a few months after you’ve had your baby (NICE 2019b). This is just to be on the safe side. Don’t worry if you intend to breastfeed. There are plenty of medications for high blood pressure that are safe to take while breastfeeding (August 2020, NHS 2018a, NICE 2019b).

Once your midwife has discharged you, you’ll still need to have your blood pressure checked. You should be given a care plan for follow-up appointments once you’re at home with your baby. This will include who you'll need to see and how often you'll need to see them (NICE 2019b).

If you had pre-existing high blood pressure, it’s unlikely to go down after you’ve had your baby (Folk 2018). You may continue to need medication (NICE 2019b).

Keeping active and eating well during your pregnancy will help you to stay healthy whatever your blood pressure level (NHS 2018a, NICE 2019b). If you have high blood pressure in pregnancy, it helps to keep your salt intake low, as this can reduce blood pressure (NHS 2018a, NICE 2019b).

Find out more about exercising in pregnancy and following a healthy diet.