What's a Healthy Blood Pressure During Pregnancy?

You might not give your blood pressure a second thought when that cuff is slapped on during your annual check-up. But a normal blood pressure during pregnancy is key to keeping you and your baby healthy.

Maintaining a normal blood pressure during pregnancy is important for mother and baby. (Image: LumiNola/iStock/GettyImages)

If you're pregnant, here's why you should keep an eye on your blood pressure readings, and what's a healthy range to aim for.

Risks of High Blood Pressure During Pregnancy

Blood pressure, which is defined as the blood's force against the arterial walls, is reported using two numbers: the systolic pressure, recorded when the heart is actively pumping blood through the arteries and the diastolic pressure, taken when the heart is at rest between beats.

Blood pressure is carefully monitored in pregnancy for two reasons, says Kjersti Aagaard, MD, PhD, a professor of ob-gyn medicine at Baylor College of Medicine. "First, because not every woman seeks or is able to obtain regular healthcare between pregnancies, some may develop chronic high blood pressure (or hypertension) when they aren't pregnant and might not be aware of it," she explains. For this reason, it's not uncommon to be diagnosed with chronic hypertension for the first time either early on or even midway through a pregnancy.

The second reason a pregnant woman's pressure is watched so closely is so doctors can keep an eye out for preeclampsia, sometimes called gestational hypertension, which can cause severe complications in both the mother and fetus, per the American College of Obstetricians and Gynecologists (ACOG). "Preeclampsia is high blood pressure combined with 'leaky' kidneys, which can range from more mild to a very severe disease with features including a risk of seizures and liver and platelet cell complications," says Dr. Aagaard.

High blood pressure in pregnancy also raises the risk of preterm labor, fetal growth restriction and placental abruption, according to ACOG.

Low blood pressure during pregnancy may also be of concern, since this can result in dizziness. Also, a sudden drop in pressure of 20 points or more, even within normal ranges, can cause problems, including dizziness and fainting, and may be deadly if the falling blood pressure can't be halted.

What's a Healthy Range?

According to the Mayo Clinic, a normal blood pressure during pregnancy is below 120/80, although some doctors prefer to see readings lower than 115/75.

Prehypertension occurs when the blood pressure reading is between 121/80 and 139/ 89. High blood pressure is defined as anything above 140/90.

Low blood pressure occurs when the reading drops below 90/50. A diagnosis of high or low blood pressure can be made using either the systolic or diastolic reading if only one of the two measurements is outside of normal range.

During pregnancy, a woman experiences changes in blood pressure as a side effect of the increase in blood volume that occurs to support the developing baby. The most significant change in blood pressure is usually a drop in systolic pressure of five to 10 points and a drop in diastolic pressure of 10 to 15 points over the first 24 weeks of pregnancy, explains the Mayo Clinic. According to the March of Dimes, about 8 percent of women experience high blood pressure during pregnancy instead of following the normal pattern of lower blood pressure.

Monitoring Your Blood Pressure During Pregnancy

During pregnancy, blood pressure levels are an important indicator of potential problems, so the doctor typically takes a reading at each prenatal visit. Home blood pressure monitors can be used between doctor's visits to keep track of blood pressure changes that might otherwise go unnoticed. Women who have high blood pressure before pregnancy, are at risk of preeclampsia or develop high blood pressure while pregnant are often advised to keep track of it at home.

"At-risk women can and should measure their blood pressure at home, record it daily or a couple of times a week and bring these numbers to their prenatal visits," recommends Dr. Aagaard.

By working with your midwife or physician to both interpret blood pressure changes, recognize dangerously high pressure when it occurs and adjust medicines for situations of chronic hypertension, outcomes for both moms and babies can be greatly improved, she adds.

Controlling High Blood Pressure

Some methods of maintaining blood pressure, such as embarking on a new exercise program, may not be appropriate for pregnant women. That's why women who develop blood pressure outside of the normal range during pregnancy may receive a prescription for medication to control it. For women whose blood pressure goes far outside the normal range, a physician may recommend bed rest for the final weeks or months of pregnancy.

"Getting regular care between pregnancies to diagnose chronic hypertension is crucial so that good blood pressure control can start before conception," urges Dr. Aagaard. And beyond pregnancy complications, there are known risk factors for chronic hypertension, such as obesity and diabetes, which can be mitigated by major lifestyle changes. "Good metabolic and vascular health is key — and to improve both at the same time, try limiting fat, sugar and sodium in your diet and adding in regular exercise and sleep," she suggests.

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