High Blood Pressure in Pregnancy

What is pregnancy-induced high blood pressure?

The body goes through many changes during pregnancy. There are changes to the heart, blood vessels, and the amount of blood in the body doubles. Because of these changes, blood pressure often increases in early pregnancy and then drops in later stages of pregnancy.

Sustained high blood pressure in pregnancy, whether it starts before or during the pregnancy, is a serious problem that can affect both your health and the health of your unborn baby. We’ll discuss what it means to have high blood pressure in pregnancy, pregnancy-induced high blood pressure, the symptoms you may feel, and how it can be diagnosed, treated, or even prevented.

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Dr. Kevin O. Hwang has been treating patients for high blood pressure and other medical problems since 2005 as a board-certified internal medicine physician. He also conducts research and teaches medical students and residents at UTHealth McGovern Medical School in Houston. Follow his blog at KevinHwang.com

Do you have pregnancy-induced HBP?

Pregnancy-induced high blood pressure (also called gestational hypertension) is when a woman with normal blood pressure before pregnancy has high blood pressure after the 20th week of pregnancy. It is diagnosed if the systolic blood pressure (top number) is 140 or above and/or the diastolic blood pressure (bottom number) is 90 or above. Pregnancy-induced high blood pressure affects 6 to 10% of pregnant women.

You may also experience symptoms like:

• Swollen feet

• Headache

• Breathlessness

• Vision problems

These symptoms usually suggest a dangerous complication of pregnancy-induced high blood pressure called preeclampsia.

The risk of pregnancy-induced high blood pressure and preeclampsia is highest if you have had preeclampsia before, if you have a family history of preeclampsia, or if you are pregnant with twins or more. The risk is also higher for older women, obese women, and those with additional medical conditions.

This guide is for women who are pregnant or are thinking about becoming pregnant.

Normal BP changes in pregnancy

Your heart, blood vessels, and blood volume change a lot during pregnancy. Why? To nourish and grow your unborn baby. The amount of blood in your body doubles, and so does the work of your heart muscle. To accommodate the extra blood and keep your blood pressure normal, your blood vessels relax.

These changes happen at slightly different stages. Blood pressure drops a little in the second trimester as the blood vessels relax. By the third trimester, most pregnant women see a slight and normal increase in blood pressure.

High blood pressure in pregnancy

Young women in their childbearing years can have high blood pressure before becoming pregnant. This is called “chronic hypertension.” Talk to your healthcare provider if you have high blood pressure and you’re hoping to get pregnant. If you’re already taking blood pressure medications, you’ll want to be sure that they are safe for you and your unborn baby.

Some women with normal blood pressure before pregnancy or during early pregnancy get high blood pressure in the second half of pregnancy. This is pregnancy-induced hypertension.

Whether you have high blood pressure or not, it will be measured at every pregnancy check-up. If your blood pressure was normal early on but then goes above 140/90 on two separate readings, then you have pregnancy-induced high blood pressure. Either the top number or the bottom number can be high. It doesn't have to be both. For example, 148/82 would be high, but so would 136/96.

Pregnancy-induced high blood pressure usually goes away after you give birth, but it can cause problems for mom and unborn baby up until after the baby is born. Some women will also be more at risk of having high blood pressure after their pregnancy than they would have been before.

Risks of high blood pressure in pregnancy

For mom

High blood pressure during pregnancy puts you at risk of:

• Stroke

• Seizures

• Heart attacks

• Breathing problems (fluid in the lungs)

• Fluid in other parts of your body (kidney problems)
  It can also put you at risk of a serious complication called placental abruption (when the placenta tears away from the womb) and complications when giving birth.

For baby

High blood pressure can also affect your unborn baby’s growth and health. When the mom’s blood pressure runs high, this affects how much oxygen and nutrients are delivered to the growing baby. Unborn babies affected by high maternal blood pressure are more likely to be born preterm and underweight.

For the birth

Pregnancy-induced hypertension raises your risk of having an early delivery or a C-section.

What is preeclampsia?

Pregnancy-induced high blood pressure can turn into preeclampsia. You’ve probably heard of this term, but may not know exactly what it means. Preeclampsia is when abnormally high blood pressure in pregnancy starts to affect important organs. This can include your:

• Brain

• Lungs

• Kidneys

• Liver

• Blood’s ability to clot

Signs of preeclampsia include:

• Abnormally high protein levels in your urine (this is a sign of kidney issues and is one of the reasons a urine sample is taken at every check-up)

• Abnormal liver or kidney tests

• Pain in the upper part of your abdomen

• Severe, long-lasting headache

• Disturbed vision (specifically, flashes of light or dark spots in your vision)

• Stroke

• Confusion

• Difficulty breathing

• Swelling in your face or hands

• Sudden weight gain

• Easy bleeding or bruising caused by low blood platelets

Your preeclampsia risk is higher if:

• You had high blood pressure before pregnancy

• This is your first baby

• You’re 40 years or older

• You’re having more than one baby

• You had in vitro fertilization to get pregnant

Having certain health conditions before pregnancy also puts you at risk of having preeclampsia. These include:

• Diabetes

• Lupus

• Chronic kidney disease,

• Obesity (a body mass index of 30 or higher)

Eclampsia and HELLP syndrome

Pregnancy-induced high blood pressure and preeclampsia can lead to serious and life-threatening conditions like eclampsia and HELLP syndrome.

• Eclampsia: This is when blood pressure in pregnancy rises so high that it causes seizures or coma in the mother. Sixty percent of eclampsia comes on during pregnancy, 20% during delivery, and 20% after delivery.

• HELLP syndrome: This acronym stands for hemolysis, elevated liver enzymes, and low platelet count. In this condition, your body destroys its own red blood cells, liver cells are damaged, and you may bleed too easily. Seventy percent of cases happen during pregnancy and 30% after delivery.

The terms “preeclampsia” and “eclampsia” sound like you need to have preeclampsia before getting eclampsia. But that’s not always true. Some women with eclampsia don’t have any symptoms of high blood pressure or preeclampsia before they start experiencing seizures. The same thing goes for HELLP syndrome. It can appear without warning.

Luckily, these conditions are rare. Eclampsia happens in less than 0.1% of pregnancies in the United States, while HELLP happens in 0.1-0.2 % of all pregnancies. Rates are higher for black and some latino women, as well as women who have pregnancy-induced high blood pressure and preeclampsia.

Preventing HBP in pregnancy

Preventing high blood pressure before pregnancy will help lower the risk of high blood pressure when you do become pregnant. In fact, the healthier you are before becoming pregnant, the healthier and easier your pregnancy will be. Healthy habits to form before pregnancy include:

• Eating well for your heart

• Maintaining a healthy weight

• Exercising regularly (brisk walking or cycling for at least 2.5 hours every week)

• Quitting smoking

• Keeping alcohol intake within safe limits

Other medical conditions, like diabetes, can also increase your risk of high blood pressure. Healthy lifestyle practices and regular check-ups can lower this risk, but probably not forever.

Whether you have high blood pressure before you get pregnant or you develop it while pregnant, one thing is for sure: regular checkups throughout your pregnancy will keep you and your unborn baby healthy.

Treating high blood pressure in pregnancy

Is treatment necessary?

Your healthcare provider won’t always recommend medications for high blood pressure during pregnancy.

The American College of Obstetricians and Gynecologists recommends that pregnant women with severe high blood pressure take medication to lower their blood pressure. “Severe high blood pressure” is when the systolic blood pressure is 160 or higher and/or the diastolic BP is 110 or higher. Between 140-159 systolic, and 90-109 diastolic, the science is less clear. If you have symptoms like headache and blurred vision you might need treatment.

Are blood pressure medications safe during pregnancy?

This is the million dollar question. All blood pressure-lowering medications cross the placenta and get into your baby’s bloodstream. But, not treating high blood pressure in pregnancy can have harmful results for mom and baby.

The concern with treating high blood pressure in pregnancy is that lowering blood pressure too quickly, and the medications themselves, can cause low birth weight. But large studies have not shown consistently whether or not this is a real concern.

A 2002 analysis of 34 studies involving 2,640 women showed that high blood pressure medications in pregnancy were linked to low birth weight babies. But, a 2018 Cochrane review of data from 5,909 women in 58 trials, and a 2017 meta-analysis of 1,166 women across 15 studies, both found that medications for mild to moderate pregnancy-induced high blood pressure did not increase the risk of low birth weight for the baby.

Healthcare professionals are also not sure whether treating high blood pressure in pregnancy actually lowers risk of birth complications, stroke, or preeclampsia. The results of the 2018 Cochrane review and the 2017 meta-analysis show that treating high blood pressure in pregnancy lowers the risk of severe high blood pressure, but does not lower the risk of birth complications or preeclampsia.

But, a 2015 international, multi-center study of 987 women found that better control of high blood pressure in pregnancy was linked to lower rates of severe hypertension and (in a 2016 follow-up analysis) better outcomes for the baby and the mother (better birth weight and less birth complications).

Which BP medications are safest in pregnancy?

Studies show that these three blood pressure medications are generally safe for treating high blood pressure in most pregnant women. They all lower blood pressure by relaxing your blood vessels.

• Methyldopa has the longest and most reassuring track record of safety in pregnancy.

• Labetalol slows your heart rate, allowing your heart to relax.

• Nifedipine only needs to be taken once a day in the extended-release form.

The research is not definitive for the majority of other BP medications. Experts are unable to confidently recommend or advise against using them to treat high blood pressure in pregnant women.

Research shows that some blood pressure medications are definitely not safe in pregnancy because they harm the baby. These unsafe medications include the following.

• Angiotensin converting enzyme inhibitors (ACE-I): Benazepril, captopril, enalapril, fosinopril, lisinopril, moexipril, perindopril, quinapril, ramipril, trandolapril

• Angiotensin II receptor blockers (ARB): Azilsartan, candesartan, eprosartan, irbesartan, losartan, olmesartan, telmisartan, valsartan

• Direct renin inhibitors: Aliskiren

• Aldosterone antagonists: Eplerenone, spironolactone

What about other treatments?

Bed rest is not typically recommended for pregnant women with high blood pressure. This is because it isn’t practical for most women and it can cause other problems like loss of strength, bone thinning, and blood clots. In some situations though, it may be recommended. This includes if you are diagnosed with preeclampsia in the third trimester. You and your provider will decide together what is best for you.

You may hear that people with high blood pressure cut salt from their diet. Salt restriction is often recommended for non-pregnant people with high blood pressure but is not advised when you are pregnant. This is because cutting out salt can actually lower the amount of blood flowing around your body and to your baby. This is not a good idea when you’re busy growing a whole human.

Keep in mind

There is much more research into high blood pressure in non-pregnant women than in pregnant women. There also isn’t much research that compares the safety of one blood pressure medication to another during pregnancy.

Pregnant women of color have higher risks of maternal complications before, during and after birth, and higher rates of death, but have been historically underrepresented in medical research. They have higher rates of heart disease, strokes and preeclampsia, so more research is needed into the causes and best treatments for non-white and non-Asian women.

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