What is low blood pressure in pregnancy

Having your blood pressure checked regularly during pregnancy is an important part of your antenatal care.

How will my blood pressure change in pregnancy?

The changes to your body caused by pregnancy also affect your blood pressure. Increased levels of progesterone and other hormonal changes allow the walls of your blood vessels to relax and widen, which tends to cause your blood pressure to lower. Your blood pressure could decrease to its lowest level mid-pregnancy, but then return to pre-pregnancy levels as you get closer to the birth of your baby.

How is my blood pressure measured?

A blood pressure test measures how strongly the blood pushes against the walls of your arteries. This is commonly done using an automatic device, or sometimes a sphygmomanometer. A cuff is placed around your upper arm and pumped up to restrict the blood flow; this may feel uncomfortable, but won’t last long. The pressure in the cuff is then gently released and your pulse is detected digitally, using sensors, or manually with a stethoscope. Two measurements are taken and these give your blood pressure reading, which will be recorded like this, for example: 110/70.

The first number is your “systolic blood pressure” and measures the pressure when your heart pushes blood out and around your body. The second number is your “diastolic blood pressure” and this is the pressure recorded when your heart rests between beats

Low blood pressure (known as hypotension) is categorized if your reading is 90/60 mm Hg or lower. Low blood pressure in pregnancy is normal and is caused by the rapid expansion of the circulatory system.

Symptoms of low blood pressure in pregnancy

If you recognize the following symptoms then you could be experiencing low blood pressure: feeling dizzy or lightheaded. Low blood pressure usually returns to your pre-pregnancy level after you've given birth and isn’t typically treated with medication unless symptoms are severe. Talk to your midwife or doctor if you are concerned about symptoms of low blood pressure.

High blood pressure in pregnancy

High blood pressure (known as hypertension) is categorised in three ranges:

• Mild: your blood pressure is between 140/90 and 149/99 mm Hg. If you are in this range you won’t need any treatment but you are likely to be monitored regularly.
• Moderate: your blood pressure is between 150/100 and 159/109 mm Hg.
• Severe: your blood pressure is 160/110 mm Hg or above.

Some women may already have high blood pressure before they get pregnant, but in others it can develop during pregnancy. Different terms are used for high blood pressure that develops at different stages of pregnancy:

Pre-existing hypertension

If you had high blood pressure before you got pregnant, it was present at your first antenatal appointment, or it developed before 20 weeks, this is known as pre-existing hypertension.

Gestational hypertension

High blood pressure that develops after 20 weeks of pregnancy is known as gestational hypertension. Your urine sample will not show the presence of excess protein (a sign of a serious condition called pre-eclampsia, discussed below).

Pre-eclampsia

Hypertension that develops after 20 weeks of pregnancy and is associated with signs that your organ systems are not functioning properly, including protein in the urine, is a condition called pre-eclampsia.

Symptoms of high blood pressure in pregnancy

It’s important that you attend each antenatal appointment so that routine blood pressure and urine tests can be done because, unless there are accompanying symptoms, you may not notice any changes in your blood pressure.

Hypertension can be an early sign of pre-eclampsia. Seek medical advice immediately if you notice any of the following symptoms: swelling of your face, hands or feet especially if sudden, severe headache that won’t go away, visual disturbances such as blurring or flashing lights, pain just below the ribs or shoulder, nausea and vomiting in the second half of pregnancy, sudden weight gain, difficulty breathing, and feeling very unwell.

What if I am already taking medication for high blood pressure?

If you are already taking medication to treat high blood pressure it’s important that you talk to your doctor if you want to start trying for a baby or if you discover that you are pregnant as they may need to change your medication - this is because your doctor may want to change your medication as some blood pressure lowering medicines are not suitable to take during pregnancy.  An alternative medicine may be prescribed however, it is important to never stop taking medicines until you have spoken to your GP or midwife.

What problems can be caused by having high blood pressure in pregnancy?

High blood pressure in pregnancy poses risks for both mum and baby. There may be decreased blood flow of oxygen and nutrients through the placenta leading to poor foetal growth and an increased chance of preterm delivery and low birth weight. It can increase the risk of placental abruption - a condition where the placenta detaches prematurely from the wall of the uterus and which requires emergency treatment.

Poorly controlled blood pressure can lead to strain and damage to the mother’s vital organs such as the heart, liver and kidneys and raise the risk of stroke.

Pre-eclampsia is a serious condition that typically develops in the third trimester. Women with pre-existing or gestational hypertension are more likely to develop it and will be advised to be very aware of the symptoms of pre-eclampsia and to seek urgent medical advice should they develop them.

Women with pre-existing hypertension will be prescribed low dose aspirin from 12 weeks gestation until birth to reduce the risk of developing pre-eclampsia.

What is considered too low of blood pressure in pregnancy?

Is low blood pressure OK in pregnancy?

What is a dangerously low blood pressure?