Chronic hypertension is estimated to complicate up to 5% of pregnancies. To establish this diagnosis, hypertension should antedate the pregnancy or be evident before 20 weeks’ gestation to differentiate it from pregnancy-related hypertension. This distinction can be problematic when the initial presentation is after 20 weeks, but chronic hypertension is confirmed if the blood pressure remains elevated beyond 12 weeks’ postpartum. Risk factors for chronic hypertension include older maternal age, African-American race, and obesity. While essential hypertension is by far the most common cause, secondary causes should be sought when clinically indicated.
Women with chronic hypertension are at increased risk for adverse maternal and perinatal outcomes. Superimposed preeclampsia develops in up to 20% of women with mild hypertension, but the risk increases up to 50% when there is severe baseline hypertension (160/110 mm Hg or higher) and may be even higher when there is evidence of end-organ damage. When preeclampsia is superimposed on chronic hypertension, there is a tendency for it to occur at an earlier gestational age, be more severe, and impair fetal growth. Women with chronic hypertension are also at increased risk for placental abruption, cesarean delivery, preterm birth, and perinatal mortality.
Ideally, women with chronic hypertension should undergo a preconceptional evaluation to detect end-organ damage, assess the need for antihypertensive therapy, and discontinue teratogenic medications. The specific tests ordered may vary depending on the severity of the hypertensive disorder, but an evaluation of kidney and cardiac function (eg, 24-hour urine protein and maternal echocardiogram if mother takes medications) is appropriate.
If the woman is not known to have chronic hypertension, then initiation of antihypertensive therapy in pregnant women is indicated only if the blood pressure is sustained at or above 160/105 mm Hg or if there is evidence of end-organ damage. Treatment of hypertension has not been demonstrated to improve pregnancy outcomes, but it is indicated in women with significant hypertension for long-term maternal cardiovascular health. Although methyldopa has the longest record of safety in pregnancy, nifedipine and labetalol are also acceptable, and these three agents are recommended above all others when initiating therapy in pregnancy. Care must be taken not to excessively reduce the blood pressure, as this may decrease uteroplacental perfusion. The goal is a modest reduction in blood pressure and avoidance of severe hypertension.
If a woman with mild chronic hypertension is stable on a medical regimen when she becomes pregnant, it is usually appropriate to continue this therapy, although the benefits of doing so are not well established. Angiotensin-converting enzyme (ACE) inhibitors and angiotensin receptor blockers, however, are contraindicated in all trimesters of pregnancy. These medications are teratogenic in the first trimester and cause fetal hypocalvaria and acute kidney injury in the second and third trimesters.
When there is sustained severe hypertension despite multiple medications or significant end-organ damage from hypertensive disease, pregnancy is not likely to be tolerated well. In these situations, therapeutic abortion may be appropriate. If the pregnancy is continued, the woman must be counseled that the maternal and perinatal risks are appreciable, and complications such as superimposed preeclampsia and fetal growth restriction should be anticipated.
American College of Obstetricians and Gynecologists; Task Force on Hypertension in Pregnancy. Hypertension in pregnancy. Obstet Gynecol. 2013 Nov;122(5):1122–31.
et al. Blood pressure profiles across pregnancy in women with chronic hypertension. Am J Perinatol. 2016 Oct;33(12):1128–32.
et al. Pregnancy outcomes in women with preeclampsia superimposed on chronic hypertension with and without severe features. Am J Perinatol. 2017 Mar;34(4):403–8.