Checking her blood pressure
Blood pressure (BP) refers to how hard the blood is 'pushing' on the walls of the major blood vessels as it is pumped around the body by the heart. The pressure is measured in millimetres (mm) of mercury (a liquid silver metal, which has the chemical symbol Hg), so blood pressure measurements are expressed as a number followed by mmHg. We will show you how to measure blood pressure in Section 9.7.1.
Doctors and nurses call the top number the systolic pressure (pronounced 'siss toll ick'). They call the bottom number the diastolic pressure (pronounced 'dye ass toll ick').
A blood pressure measurement is two numbers written one above the other. The top number tells you the woman's blood pressure at the moment when her heart 'beats' and pushes blood out into her body. The bottom number tells you her blood pressure when her heart relaxes between each beat, so it can refill with blood.
Healthy blood pressure
Normal blood pressure stays between 90/60 mmHg (you say this aloud as 'ninety over sixty millimetres of mercury',) and below 140/90 mmHg ('one hundred and forty over ninety millimetres of mercury'). It does not go up much during pregnancy.
High blood pressure is known medically as hypertension and is a warning sign. The woman has high blood pressure if either of these is true:
- The top number is 140 or above.
- The bottom number is 90 or above.
Very low blood pressure (less than 90/50 mmHg) is also a warning sign, which is usually caused only by heavy bleeding or shock (a dangerous reduction in blood flow throughout the body). This is a very dangerous situation.
A woman with very low blood pressure should be referred to the nearest health centre immediately.
The heart is like a pump, pumping blood through the body. High blood pressure means that the heart must work harder to press the blood through tight or shrunken blood vessels (veins and arteries). Blood pressure numbers show how hard the blood has to press. Note that blood pressure is not the same as pulse. You can have a slow pulse with a high blood pressure.
It is very important to check the mother's blood pressure at every antenatal visit and refer her to a health centre if it is too high.
When a woman has high blood pressure during pregnancy, it is harder for her blood to bring food and oxygen to the baby via the placenta. (You learned about this in Study Session 5.) The baby then grows too slowly. Very high blood pressure can also cause the woman to have kidney problems, bleeding in the uterus before birth, or bleeding in the brain (stroke). It can also be a sign of pre-eclampsia, which can cause premature birth, bleeding, convulsions, or even death for the mother.