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 7 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 effects 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 i.e. 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 (BP)?
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 i.e. an elevated blood pressure even before they become pregnant. They need extra close monitoring because any 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 healthcare practitioners is that when this occurs, the mother may already have had problems with hypertension before she conceived, but this was never diagnosed. In mothers who have existing hypertension, they are at an increased risk of developing Preeclampsia.
Normal blood pressure reading
High Normal BP
Mildly elevated BP
Reading between 140/90–159/99
Moderately high BP
Reading between 160/100–179/109
Severely high BP
Reading between 180/110 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, which can lead to bleeding and an interruption of blood and oxygen flow to the baby
An on-going 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 going to the baby, which 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 preeclampsia is present, then this generally occurs within the second half of pregnancy.
A mother is diagnosed with pregnancy-induced hypertension (PIH) when she develops high blood pressure for the first time after her 20th week of pregnancy.
Generally by six weeks after birth or before, there is a return to normal blood pressure readings. If there is not, investigations and close monitoring is recommended.
Treatment for high blood pressure during pregnancy
A number of factors need to be considered when planning for care:
How high the BP readings are – an isolated reading is not as significant as when two elevated readings or more are noted.
The location of the mother and how far she lives from medical support and monitoring. Living in a rural or isolated location is more risky, especially when there is limited access to obstetric care and services.
How many babies a mother is carrying – twins and multiples increase the associated risks of having a high BP.
Each individual mother’s obstetric history.
For best treatment options refer to a medical practitioner.
When does a high blood pressure become something else?
When there is a combination of high blood pressure and protein in the urine, then there is a diagnosis of preeclampsia. Check the Preeclampsia section for more comprehensive information. A combination of high BP, protein in the urine, swelling, and sudden weight gain are all concerning signs.