Having an elevated blood pressure (BP) during pregnancy is not uncommon. The amount of blood the heart needs to pump to all the organs increases steadily until the stage of around 20 weeks when it is pumping approximately seven litres every minute. If the heart pumps too rapidly, palpitations can be felt as each contraction of the heart is not as forceful or coordinated as it needs to be. The combination of extra blood volume and more efficient pumping action by the heart means that the blood pressure should actually be affected more than it is. However, during pregnancy, protective factors in the blood vessels make them more dilated and elastic. This means that in most women, problems with high blood pressure do not occur. Their body compensates for all the extra blood flow and they manage just fine.
Progesterone, the relaxing hormone of pregnancy, helps to support changes in the blood vessels. Although most of its effects are beneficial, not all are. The other side to the progesterone story is that haemorrhoids and varicose veins are common. These are the unwanted side effect of having more dilated blood vessels, and for many women can become a nagging and constant reminder that pregnancy is not always the wonderful time of their lives they d hoped it would be.
What is High Blood Pressure Anyway?
High blood pressure or hypertension occurs when the pressure of the blood is too high as it is being pumped along the arteries. With each beat of the heart, the left ventricle (one of the four major chambers) contracts and pushes oxygen laden blood out via the aorta. If the pressure of the blood as it is pumped out is too high, this has a flow on effect as it is forced along the walls of the arteries. When blood pressure is measured, the first or higher reading the systolic measurement, records the pressure in the arteries as the heart is contracting. The second or diastolic reading, measures the pressure in the arteries when the heart is at rest, pausing between each heartbeat. Blood pressure is always recorded as millimetres of mercury e.g. the amount of pressure it takes for the column of mercury to rise. The old fashioned blood pressure cuff and a sphygmomanometer are still thought to be the most accurate way of measuring BP despite today's technology.
What's a Normal Blood Pressure?
A normal blood pressure is generally a reading less than 140/90. This is dependent on a mother? size, activity and how well hydrated she is. Some women have essential hypertension e.g. an elevated blood pressure even before they become pregnant. They need extra close monitoring because an additional rise may mean they or their baby are at additional risk. Others develop high blood pressure before they progress to 20 weeks gestation. The general assessment from health care practitioners is that when this occurs, the mother may already have had problems with hypertension before she conceived but this was not diagnosed. In mothers who have existing hypertension, they are at an increased risk of developing Preeclampsia.
|Normal blood pressure reading||Below 140/90|
|Mildly elevated BP||Reading between 140-90 149/99|
|Moderately high BP||Reading between 150-100 159-109|
|Severely high BP||Reading between 160/110 or higher|
Risks of Having High Blood Pressure During Pregnancy
- An increased risk of placental abruption where the placenta or part of it dislodges from the uterine wall. This can lead to bleeding and an interruption of blood and oxygen flow to the baby.
- An ongoing problem with hypertension in a mother after her baby is born.
- Women who progress from having hypertension to having Preeclampsia can be at an increased risk of developing cardiovascular disease in later life.
- A decrease in the blood flow which is going to the baby. This can lead to an increased risk of premature birth and associated problems.
What Normally Happens?
During pregnancy, there is usually little change in a mother's blood pressure within the first 30 weeks of gestation. A slight rise from this stage to full term is common and generally nothing to be concerned about. If pre-eclampsia is present then this generally occurs within the second
Last Published* November, 2021
*Please note that the published date may not be the same as the date that the content was created and that information above may have changed since.