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Cases of high blood pressure during pregnancy rose sharply from 1970 to 2010, according to a recent study published in the journal Hypertension.

A key driver of the change: more women giving birth at older ages, says study author Cande Ananth, professor and vice chair of academic affairs and chief of the division of epidemiology and biostatistics in the department of obstetrics, gynecology and reproductive sciences at Rutgers Robert Wood Johnson Medical School.

The study also found that black women are more likely to have high blood pressure during pregnancy than white women.

High blood pressure during pregnancy — defined in this study as hypertension diagnosed before pregnancy or in the first five months — threatens the health of both mother and baby. It’s linked with an increased risk of preterm birth, low birth weight and severe complications for the mother, such as preeclampsia (a potentially fatal condition defined by high blood pressure during pregnancy plus signs of liver or kidney damage).

Here’s what you need to know about this study and about your blood pressure if you’re pregnant or thinking of becoming pregnant.

What the study found

Researchers reviewed Centers for Disease Control and Prevention data on more than 151 million women who gave birth in hospitals between 1970 and 2010. (The researchers looked only at data through 2010 because the CDC’s data collection on hospitalizations changed substantially after that year.)

The research revealed that over the 40 years in question, the rate of hypertension during pregnancy increased by about 6 percent each year — from just 0.11 percent in 1970 to 1.52 percent in 2010.

On average, during the period studied, the prevalence of hypertension in pregnancy was 0.53 percent among white women, and 1.24 percent in black women.

Rates of hypertension during pregnancy have been increasing in part because more women are giving birth later in life, researchers say, and the risk of high blood pressure rises with age. According to the CDC, the average age of first birth in 1970 was 21.4; in 2017, it was 26.8.

The study authors also took into account data from a different CDC source on national smoking and obesity rates, because both are significant risk factors for high blood pressure. They wanted to see whether either may have played a role in the study’s findings. But the researchers observed only small effects from these factors.

One limitation, the researchers note, is that the definition of high blood pressure has changed over time. Since 1970, the threshold at which someone can be diagnosed with hypertension has gone down. That alone may have caused at least some of the rise in rates, Ananth says.

And the study doesn’t indicate why black and white mothers have such different rates. But one theory is that chronic stress may contribute, especially the stress that arises from confronting racism.

“People are leaning towards the fact that this could be related to the stress of being a minority population in the United States,” says James M. Roberts, an investigator with the Magee-Womens Research Institute and a professor in the department of obstetrics, gynecology and reproductive sciences at the University of Pittsburgh. He wasn’t involved in the new study.

What to do to cut risk

If you already have high blood pressure and you’re thinking about having a baby, talk with your doctor well before you become pregnant, Roberts says. That way, if you’re on medication, you can figure out whether the drugs you’re taking are safe for pregnant women. You may need to switch medications.

Lifestyle changes can help you get your blood pressure down before conceiving. Getting regular exercise, losing weight if you need to, quitting smoking, abstaining from alcohol and improving your diet can all help, Ananth says.

If you do have high blood pressure while you’re pregnant, Roberts recommends finding a doctor who specializes in high-risk pregnancies, and working with that physician to keep a close eye on your blood pressure. Monitoring your own blood pressure at home may help. Ask your doctor what level to aim for and at what level you should call to alert them.

Know the warning signs of preeclampsia. Key symptoms to look out for: persistent headaches, abdominal pain, vision changes such as blurred vision or seeing spots or light, swelling of the face or hands, nausea or vomiting, sudden weight gain, and trouble breathing.

If you notice any of these symptoms, call your doctor. If you’re diagnosed with preeclampsia, your doctor may recommend blood pressure medication and close monitoring either in or outside of the hospital. Depending on how far along you are in the pregnancy, your doctor may also suggest inducing labor.

Also, be aware that in many cases, preeclampsia won’t have any obvious symptoms. That’s another reason it’s critical to receive regular prenatal care, Roberts says. That way, your provider can perform urine and blood tests that can reveal liver or kidney dysfunction.

 Copyright 2019, Consumer Reports Inc.

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