Pregnancy and hypertension

Sandra Tsai, MD, MPH is a clinical assistant professor in the Preventive Cardiology Clinic, the Women’s Heart Health Clinic, and Stanford Primary Care. BeWell spoke with Dr. Tsai to learn more about hypertension in pregnancy and its implication for a woman’s future cardiovascular health.

Can you explain what hypertension is, and the different types/severity of hypertension that can occur during pregnancy?

Hypertension is defined as a systolic blood pressure (BP) of ≥140 or a diastolic BP ≥90.

Hypertension in pregnancy has four categories: 1) preeclampsia/eclampsia, 2) chronic hypertension (of any cause), 3) chronic hypertension with superimposed preeclampsia, and 4) gestational hypertension. The more severe forms of hypertension in pregnancy are termed preeclampsia and eclampsia; these will manifest other signs and symptoms including protein in the urine and neurologic changes such as seizures. Chronic hypertension is defined as hypertension pre-pregnancy, before 20 weeks gestation, or hypertension that persists ≥12 weeks postpartum. Gestational hypertension is diagnosed when a pregnant woman has new onset hypertension without signs of organ dysfunction at or after 20 weeks of gestation or up to 12 weeks postpartum.

Why should hypertension in pregnancy be of concern to us? What risks does it pose to a woman's long-term health?

Hypertension in pregnancy — especially the more severe forms (preeclampsia and eclampsia) —  increases the risk for complications such as placenta abruption, acute kidney injury, and death. Longer-term, women diagnosed with hypertension in pregnancy are at risk for future cardiometabolic diseases — including hypertension, diabetes, stroke, and heart attacks. And hypertension in pregnancy is surprisingly prevalent.

How prevalent is it?

Hypertension in pregnancy is the most common complication of pregnancy. The prevalence ranges from 5-10% of all pregnancies and varies depending on the population.

How is one diagnosed with it?

A woman’s blood pressure is monitored at each prenatal visit. If the BP is ≥140/90 on two different occasions at least 4 hours apart, the OB provider will evaluate further. If the elevated blood pressure is determined to be hypertension rather than "white coat hypertension” (when the BP is only elevated in clinic but normal at home), the next step is to distinguish gestational hypertension from preeclampsia, which has a different course and prognosis.

Who is at risk for it? What are the causes? Are there lifestyle behaviors that a woman can practice to prevent it?

The causes of hypertension in pregnancy are still not fully understood. Factors that increase a woman’s risk for developing hypertension in pregnancy include preexisting hypertension, diabetes, age >40, and obesity. Some data suggest gestational hypertension and preeclampsia are independent diseases. In preeclampsia, the abnormal development of the placental vasculature early in pregnancy is well-documented. These abnormalities can result in a lack of blood flow and oxygen to the placenta. This may lead to the release of circulating factors that can cause widespread dysfunction of the maternal arteries — resulting in hypertension, protein leakage in the urine, and the other clinical manifestations of preeclampsia. Lifestyle behaviors — such as a healthy diet, regular exercise, starting pregnancy with a normal weight — may reduce, but may not entirely prevent, a woman’s risk for developing hypertension in pregnancy.

What are the treatments? Can it be managed by lifestyle alone?

If gestational hypertension, rather than preeclampsia, is diagnosed, women have weekly or twice-weekly antepartum visits to measure blood pressure and protein excretion. In gestational hypertension, the decision to start anti-hypertensives is dependent on the provider and the benefit/risk profile of the patient. Many providers will start anti-hypertensives when the SBP ≥150 or the DBP ≥95 to reduce the risk of stroke. Ten to 50 percent of women initially diagnosed with gestational hypertension go on to develop preeclampsia in one to five weeks. If the diagnosis of preeclampsia is made, the definitive treatment is delivery to prevent development of maternal or fetal complications from disease progression. The decision on timing of delivery depends on when the preeclampsia develops. If a woman is ≥37 weeks gestation, she will be scheduled for delivery. Prior to 37 weeks gestation, the risks of preterm delivery are weighed against the risks of maternal and fetal complications from preeclampsia.

The 2011 American Heart Association Guidelines on the Prevention of Cardiovascular Disease in Women highlighted the need for more attention to pregnancy-related complications. Can you speak to the importance of this?

The American Heart Association stressed the importance of taking an obstetric history because women who develop gestational hypertension and preeclampsia have an increased risk for future hypertension, heart disease, and stroke. Many physicians and patients believe that once the pregnancy is over and the hypertension resolves after delivery, the risk is over. However, this is not the case. It is important for women to know that if they develop hypertension in pregnancy, they should discuss cardiovascular preventive strategies with their physician.

You are currently conducting an intervention aimed at helping overweight and obese pregnant women who may be at risk for hypertension in pregnancy. Please tell us more about that.

I am interested in helping women maintain a healthy weight throughout pregnancy. Women who start their pregnancy with excess weight are at increased risk for gaining more weight than the Institute of Medicine recommends. If these women can remain within the weight gain guidelines, they may be at less risk of developing pregnancy complications such as gestational hypertension and preeclampsia. In collaboration with the Stanford Health Improvement Program, a weight management program tailored for pregnant woman has been developed, together with a texting program, to support healthy behaviors. Our Health-texting In Postpartum Moms study was developed to test the feasibility of using this program in a population of pregnant overweight and obese women to maintain the recommended amount of weight gain in pregnancy. We have completed enrollment in the study and plan for study completion in 2016.

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