It’s perfectly normal for your blood pressure to change a little during pregnancy. The hormone progesterone relaxes the walls of your blood vessels. This may make your blood pressure fall during your first trimester and second trimester. You may find you feel faint if you stand for too long or get up quickly with lower blood pressure.
Your blood pressure is at its lowest in mid-pregnancy and starts to rise gradually again from 24 weeks pregnant. By this time, you’ll have made an extra litre (two and a half pints) of blood, which your heart has to pump around your body.
If all is well, your blood pressure will return to its pre-pregnancy levels in the last few weeks before your baby is born
Your midwife will use a small monitor to measure and record your blood pressure at every antenatal check-up.
Before your midwife measures your blood pressure, she’ll ask you to sit down and remove any tight clothing from your arm. Then she will 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 110/70 and 120/80, although this varies a lot in pregnancy.