Hypertension (high blood pressure) in Pregnancy

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Having high blood pressure, or hypertension, during pregnancy means that your systolic blood pressure (blood pressure when the heart’s ventricles contract) is more than 140 mm Hg (mm Hg stand for “millimeter of mercury”), or the diastolic blood pressure (blood pressure when the ventricles relax) is more than 90 mm Hg. This is a little different than in non-pregnant adults, who are considered to have early high blood pressure (and, thus, a possible need for medication) if systolic pressure exceeds 130 mm Hg. During pregnancy, pressure in the range of 130-140 mm Hg is just monitored to see if it gets higher, but your doctor would not give you antihypertensive medication in such cases, because it could reduce the flow of blood through the uterus and placenta.

About 7 percent of young adults in the United States have high blood pressure. In younger adults, systolic pressure is usually higher in men than women, but women do have an increased tendency toward hypertension when they are pregnant. Whether or not you are pregnant, the risk of hypertension increases with smoking, obesity, and kidney problems.

Hypertension in pregnancy can be pre-existing or chronic. Chronic means that the high blood pressure is a continuation from high blood pressure that you had prior pregnancy. On the other hand, pregnancy can be a time when hypertension develops as a feature of certain syndromes that can develop as complications of pregnancy. One complication syndrome is called preeclampsia and another is called HELLP syndrome. In either of these syndromes, hypertension can occur as a new-onset condition, meaning that blood pressure was normal prior to pregnancy, or prior to 20 weeks gestation (midpoint of pregnancy). Alternatively, preeclampsia or HELLP syndrome may superimpose on pre-existing hypertension. Physicians classify hypertension as severe if the systolic pressure reaches higher than 160 mm Hg or if the diastolic pressure exceeds 110 mm Hg.

If you develop hypertension, symptoms include headache, dizziness, and nose bleeds, plus there can be complications particular to pregnancy, such as intrauterine growth restriction (slow growth of the fetus in the womb), low birth weight, and placental abruption (detachment of the placenta from the uterine wall) leading to severe bleeding. Other severe complications of high blood pressure include atrial fibrillation (quivering of the upper chambers of the heart), acute coronary syndrome (a heart attack), heart failure, rupture of arteries, and stroke. Over the long-term, hypertension can cause damage to multiple organs, including the heart, kidneys, and eye. On the other hand, looking at the retina of the eye with special instruments helps doctors diagnose hypertension. However, the most important test is to use a blood pressure cuff, taking at least two different readings of your pressure.

For people who have early hypertension with systolic pressure in the range of 120 -140 and diastolic in the range of 80 – 90 mm Hg, life style modification, such as exercise and weight reduction, are viable treatments. Otherwise, medications are the main focus of treatment. Medications include labetalol (which belongs to a family of drugs called beta-blockers), hydralazine, nifedipine, and sodium nitroprusside –used for emergency control of blood pressure. Nifedipine and labetalol also are used for long-term control of blood pressure, and so are other medications, including methyldopa and a family of drugs called calcium channel blockers. If your blood pressure is very high, or if you have preeclampsia, the benefits all these drugs are considered to outweigh the risks, including the risks for the fetus. Furthermore, methyldopa, labetalol and other beta-blockers (such as propranolol, atenolol, and metoprolol), calcium-channel blockers, nifedipine, and hydralazine are considered safe in nursing mothers. In cases of preeclampsia, or eclampsia (a complication of preeclampsia in which seizures develop), an agent called magnesium sulfate is given to prevent or stop seizures.

Importantly, there are some types of blood pressure-lowering drugs that you must avoid during pregnancy, such as ACE inhibitors, which can damage the fetal kidneys, and angiotensin receptor blockers. If you are taking any of these drugs to control blood pressure prior to pregnancy, it needs to be changed before you get pregnant.

David Warmflash
Dr. David Warmflash is a science communicator and physician with a research background in astrobiology and space medicine. He has completed research fellowships at NASA Johnson Space Center, the University of Pennsylvania, and Brandeis University. Since 2002, he has been collaborating with The Planetary Society on experiments helping us to understand the effects of deep space radiation on life forms, and since 2011 has worked nearly full time in medical writing and science journalism. His focus area includes the emergence of new biotechnologies and their impact on biomedicine, public health, and society.

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