Kelsey McLaughlin, PhD
Approximately 10% of pregnant women in Canada have high blood pressure during pregnancy, as discussed in our blood pressure & hypertension article. Gestational hypertension is the most common hypertensive disorder of pregnancy, impacting 8% of all pregnancies. However, there has not been as much research into understanding gestational hypertension as preeclampsia.
Let's chat about gestational hypertension.
What is gestational hypertension?
Gestational hypertension is diagnosed when a pregnant women who had normal blood pressure prior to pregnancy develops high blood pressure after 20 weeks of pregnancy. High blood pressure is defined as systolic blood pressure over 140 mmHg and/or diastolic blood pressure over 90 mmHg.
Women with gestational hypertension do not show symptoms of other organ injury - this is what differentiates gestational hypertension from preeclampsia. Women with preeclampsia also develop high blood pressure after 20 weeks of pregnancy, along with symptoms of damage to the kidneys, liver or heart.
Gestational hypertension typically develops near the end of pregnancy, and is defined as non-severe or severe:
Non-severe - systolic blood pressure between 140-159 mmHg and/or diastolic blood pressure over 90-109 mmHg
Severe - systolic blood pressure over 160 mmHg and/or diastolic blood pressure over 110 mmHg
Pregnant women with gestational hypertension usually have normal pregnancy outcomes. However, women with gestational hypertension are at higher risk of adverse pregnancy outcome, including preterm birth and small for gestational age babies, compared to pregnant women with normal blood pressure.
What causes gestational hypertension?
Understanding what causes hypertension is a million dollar question that has been long researched in non-pregnant patients. There has been less research devoted to understanding hypertension in pregnancy.
The data we have so far has helped to form the theory that abnormal function of the mom's heart and blood vessels play a role in the development of gestational hypertension.
When compared to pregnant women with normal blood pressure, women with gestational hypertension pump less blood from the heart with each beat (cardiac output) and higher levels of resistance in their arteries (total peripheral resistance). These are similar changes seen in some non-pregnant patients with hypertension. Women who go on to be diagnosed with gestational hypertension have higher blood pressures even at 10-17 weeks of pregnancy, when compared to women who continue to have normal blood pressure levels.
If we look at a more molecular level, we know that women with gestational hypertension have high levels of circulating endothelial microparticles in their blood compared to pregnant women with normal blood pressure - these are little particles released by the inner lining of the blood vessels when there is disruption or irritation of the vessels. However, the levels of these microparticles in the blood are even higher in women with preeclampsia, indicating that women with gestational hypertension may have lower levels of blood vessel irritation than women with preeclampsia.
Overall, the abnormalities in the mom's heart and blood vessels do not seem to be as severe in women with gestational hypertension as women with preeclampsia. In addition, the levels of proteins being released by the placenta into the mom's blood stream are relatively normal in women with gestational hypertension when compared to pregnant women with normal blood pressure. Arteries around the uterus also show normal blood flow in women with gestational hypertension.
This suggests that the main cause of gestational hypertension may be due solely to abnormalities of the mom's cardiovascular system, rather than a combination of the cardiovascular system and placenta. As previously discussed, pregnancy puts a large amount of stress on the mom's heart and blood vessels; too much stress could possibly lead to the development of gestational hypertension.
Risk factors for gestational hypertension
Body mass index over 25 kg/m2
Diabetes, type I or type II
History of preeclampsia in previous pregnancy
Renal or cardiac disease
Older maternal age
Symptoms of gestational hypertension
The symptoms associated with gestational hypertension are similar to symptoms observed in non-pregnant patients with hypertension. These include:
Weight gain or edema
Nausea & vomiting
Testing & investigations for gestational hypertension
Blood pressure monitoring is a standard practice for pregnant women in Canada and should be measured at clinical appointments to check for high blood pressure.
Women with high blood pressure will also be checked for other symptoms of organ injury to determine if a women has gestational hypertension or preeclampsia. This could include testing urine for signs of kidney injury and testing blood for signs of liver or other injury. Pregnant women with gestational hypertension will not show signs of additional organ injury.
When women are diagnosed with gestational hypertension, doctors will investigate how well mom’s placenta is functioning. Dysfunction of the placenta is more common in women with preeclampsia than women with gestational hypertension.
Doctors will also monitor the baby to ensure that the growth and development are normal. This includes fetal heart rate, blood flow through the umbilical cord and blood flow in the brain. Studies have shown that pregnant women with hypertension tend to have smaller babies, compared to pregnant women with normal blood pressure. These investigations will let doctors know if the baby is being impacted by mom’s high blood pressure and if early delivery should be considered to ensure the health of the baby. It is recommended that the baby’s heart rate is monitored while mom is being given drugs that lower blood pressure, to make sure the baby's heart rate is stable.
Doctors will be careful to watch that gestational hypertension doesn't progress into preeclampsia, which is considered a more severe type of hypertensive disorder. Studies have reported that over 40% of women with gestational hypertension developed additional signs of organ injury, and were subsequently diagnosed with preeclampsia.
Treatment & management of gestational hypertension
Treatment for gestational hypertension is mostly centered around controlling mom's blood pressure and preventing any harm to mom and baby.
In pregnant women with non-severe gestational hypertension, doctors will typically try to keep mom’s blood pressure between 130 - 155 mmHg systolic and between 80 - 105 mmHg diastolic. If women with gestational hypertension have other health conditions (ie. diabetes, kidney disease), her doctors may try to lower her blood pressure even further to prevent complications. Doctors will try to maintain blood pressure of women with severe gestational hypertension below 160 mmHg systolic and below 110 mmHg diastolic.
Drugs used to lower mom’s blood pressure are called ‘anti-hypertensives’. The Society of Obstetricians and Gynaecologists of Canada advises that the choice of anti-hypertensive drug should be based on the patient, any contraindications to certain types of drugs and physician experience or familiarity with these drugs.
There is evidence that some bed rest in hospital may help to prevent the development of severe hypertension and preterm birth. A combination of home and hospital care could be considered for women with gestational hypertension. If mom’s blood pressure does become severe, hospital admission is recommended.
There is not sufficient evidence to support other lifestyle changes, such as salt or calorie restriction, exercise and workload reduction for women with gestational hypertension.
Corticosteroid therapy should be considered for pregnant women with gestational hypertension who are less than 35 weeks pregnant, if delivery is possible within the next week. These drugs help to promote the maturity of the baby’s lungs and decrease the risk of adverse fetal effects.
The Society of Obstetricians and Gynaecologists of Canada recommended that women with gestational hypertension who are over 37 weeks pregnant are delivered within days. Further, The American College of Obstetricians and Gynecologists recommends delivery for women with gestational hypertension over 34 weeks of pregnancy who have any abnormal mom or baby concerns.
Prevention of gestational hypertension
Scientists hypothesize that if gestational hypertension is mainly caused by stress on the mom’s cardiovascular system, getting mom’s heart and blood vessels in good shape before pregnancy may be an effective way at preventing gestational hypertension. This would include steps to improve heart health, including regular exercise, maintaining a good blood pressure level, lowering cholesterol, eating healthy and quitting smoking. Studies have shown that exercise in pregnancy has also been shown to lower the risk of women developing hypertension.
In pregnant women with low calcium intake, calcium supplementation also lowers the risk of all hypertensive disorders of pregnancy, including gestational hypertension.
Aspirin therapy does not reduce the risk of gestational hypertension from developing in pregnant women.
Gestational hypertension is a common hypertensive disorder of pregnancy that impacts approximately 8% of pregnancies. It is hypothesized that gestational hypertension is caused by dysfunctional of mom's heart and blood vessels. Treatment for gestational hypertension is mostly entered around controlling mom's blood pressure to protect mom and baby from hypertension. Further research is needed to identify the exact cause of gestational hypertension to understand which women are at the highest risk of this disease and how to press prevent it from developing.
Every woman and every pregnancy is unique. Pregnant women should speak to their healthcare provider to ensure maternal and fetal safety. This article is meant to provide readers with current information and opinions. All medical and treatment decisions should be discussed with your healthcare provider.