Obstetrician Perth | Specialised in gestational hypertension
High Blood Pressure In Pregnancy
What is gestational hypertension?
Also known as pregnancy-induced hypertension, gestational hypertension is when high blood pressure first presents in pregnancy. This is a relatively common complication, occurring in around 10% of first pregnancies. The condition does not lead to symptoms until it is severe, and multiple adverse outcomes are possible, some of which are serious. This is the primary reason routine antenatal care ever started: to detect a problem before it becomes symptomatic, by which stage is very severe.
Common symptoms include
Sudden weight gain
Vision problems and light sensitivity
Nausea and vomiting
What are the risks of high blood pressure during pregnancy?
This condition was once called Toxaemia, but no toxin was identified so the name was changed. We now believe that ‘toxin’ may refer to the high levels of free oxygen radicals related to the immune process.
Pre-eclampsia is not an accurate name either, as it implies that it occurs before Eclampsia, which is uncommon. In Pre-eclampsia, blood pressure problems develop throughout the pregnancy. This differs from women who have high blood pressure before the beginning of the pregnancy or in early pregnancy.
Women with chronic blood pressure problems are at higher risk of developing Pre-eclampsia but as a group, they do better than women who have normal blood pressure, possibly because we tend to watch them more closely from the outset.
Pre-eclampsia will have a number of effects on both mother and child. As it is a placental problem, it can interfere with placental function leading to poor growth of the baby during the pregnancy. The baby also has a greater risk of becoming stressed during labour.
As the condition is related to the placenta, it will resolve after delivery. This means there may be a need to deliver the baby early, which may imply consequences from being premature.
In the mother, the blood pressure can be sufficiently high raise concerns about the risk of stroke.
It will affect other organ systems as well. It can cause the kidney to leak protein, which is why I will test your urine if your blood pressure becomes elevated. It can also affect liver function and the body’s capacity to produce platelets, the factor in the blood that initiates control of bleeding.
These effects on other organ systems such as the blood, kidney or liver, may dictate the need for early delivery.
Treatments for high blood pressure during pregnancy
Rest has a long history as a treatment option but little basis in science. If you spend an extended time laying down, you become lightheaded when you stand up. Laying down switches off mechanisms that the body uses to keep the blood pressure normal while standing.
Rest may lower blood pressure but is not very practical. Most importantly, it does nothing to address the cause of the blood pressure rise. So it takes away the signs but not the condition.
The condition is treatable with medication, which can be very important if the blood pressure is dangerously high. These medications have been successfully used for decades, and we are happy to utilise them when required.
Like rest, medication does not remove the underlying condition but masks the main sign of the condition. So, there is an increased need for surveillance after the medication is started. We will most likely use the medication if the condition is relatively mild. Conversely, if the condition is severe and the pregnancy is relatively early, we will use medication with the hope of allowing the pregnancy to last longer.
Monitoring blood pressure
How often we measure will relate to the current severity. It may be done several times an hour when the condition is severe. If it is mild, it may simply mean frequent antenatal visits.
There are other types of high blood pressure, including “white coat hypertension”, people who have higher blood pressure when seeing a health professional because of some underlying anxiety. I will often encourage these women, as well as women with chronic blood pressure problems, to monitor themselves at home with a blood pressure machine that can be hired or bought.
The condition can affect the placental function and so there is a need to monitor potential impact on the baby. The two main methods are:
- Ultrasound: This is a long-term test of the wellbeing of the baby, looking at the growth of the baby, the amount of fluid around the baby, and the blood flow to the placenta and within the babies circulation
- CTGs: Fetal heart rate monitoring, or CTGs, is a more acute test of the baby’s wellbeing. They show patterns of changes in the heart that indicate whether the baby is well or at risk.
The ultimate treatment is to deliver the baby. It may take a little time to resolve after, and typically, it becomes a little worse on the first day after delivery.
It is a balancing act to work out when to deliver. Eclampsia demands immediate delivery, or, at the other end of the spectrum, it may be possible to delay delivery for weeks. If the baby is early, that may be highly desirable.
The method of delivery reflects the urgency. Eclampsia would usually demand c-section, while mild cases can plan for vaginal delivery after the labour is induced.
Prevention of high blood pressure in pregnancy
High blood pressure problems in pregnancy are difficult to predict. Over the decades there have been many attempts to try to devise an early test that will predict the condition, but they generally perform poorly. The most recent and useful test looks at factors at the end of the first trimester. It will predict some, but not all, of the women who will develop earlier onset and more severe forms of the condition. This represents a small subgroup of people, and so it is of little value for most women.
Women who have had the condition before have a slightly higher risk in a second pregnancy. It occurs in 10% of first pregnancies and then again in 15% of women who had it in the first pregnancy. That means 85% of women will not have a recurrence.
Aspirin is the mainstay of prevention strategies. It needs to be given in a low dose to be effective. This is not without risk and so we need to be selective in its use.