High blood pressure (hypertension) during pregnancy is classified as one of the following:
Preeclampsia causes high blood pressure to develop during pregnancy, but it is diagnosed and treated differently from other types of high blood pressure (see Complications of Pregnancy: Preeclampsia).
Women who have chronic hypertension are more likely to have potentially serious problems during pregnancy. These problems include the following:
During pregnancy, women with high blood pressure are monitored closely to make sure blood pressure is well controlled, the kidneys are functioning normally, and the fetus is growing normally. However, premature detachment of the placenta cannot be prevented or anticipated. Often, a baby must be delivered early to prevent stillbirth or complications due to severe high blood pressure (such as stroke) in the woman.
For most women with mild high blood pressure (140/90 to 150/100 millimeters of mercury [mm Hg]), treatment with antihypertensive drugs is often not recommended. Such treatment does not seem to reduce the risk of preeclampsia, premature detachment of the placenta, or a stillbirth or to improve the growth of the fetus. However, some women are treated to prevent pregnancy from causing episodes of even higher blood pressure, which require hospitalization.
For women whose blood pressure is higher than 150/100 mm Hg, treatment with antihypertensive drugs is recommended (see High Blood Pressure: Antihypertensive Drugs). Treatment can reduce the risk of stroke and other complications due to very high blood pressure. Treatment is also recommended for women who have high blood pressure and a kidney disorder. If high blood pressure is not controlled well, the kidneys may be damaged further.
Most antihypertensive drugs used to treat high blood pressure can be used safely during pregnancy. However, angiotensin-converting enzyme (ACE) inhibitors are stopped during pregnancy, particularly during the last two trimesters. These drugs can cause severe kidney damage in the fetus. As a result, the baby may die shortly after birth. Aldosterone antagonists (spironolactone and eplerenone) are also stopped because they can cause a male fetus to develop feminine characteristics. Thiazide diuretics (such as hydrochlorothiazide) are usually stopped during pregnancy. These diuretics increase the risk that the fetus will not grow as much as expected.
Last full review/revision December 2008 by Sean C. Blackwell, MD