by Michelle A. Finkel, MD
High blood pressure associated with pregnancy -- also called hypertension in pregnancy -- is defined as a blood pressure of greater than or equal to 140 mm Hg systolic (the top number in blood pressure readings) and greater than 90 mm Hg diastolic (the bottom number). It is not a disease itself, but is instead an umbrella term for a group of serious disorders that includes chronic high blood pressure (which starts before pregnancy), eclampsia, preeclampsia and a disorder called HELLP syndrome.
Hypertensive disorders of pregnancy were once called "toxemia" because scientists believed that an undiscovered toxin caused the dangerous conditions. While this theory is no longer in vogue, a clear cause of hypertensive disorders in pregnancy is still unknown. Even without a cause, however, it is still possible to ascribe general characteristics to the conditions. They are characterized by blood vessels that spasm and leak abnormally, and can vary from mild, isolated high blood pressure to very severe problems that require emergency care. Also, they almost always occur in the third trimester of pregnancy.
During a normal pregnancy your blood pressure drops, in part because all the blood vessels dilate (expand), lessening the force of the blood against the vessel walls. The top (systolic) number in the blood pressure reading will decrease slightly but the bottom number (diastolic) can fall considerably, beginning in the first trimester and continuing to the end of the second trimester. In the third trimester, blood pressure will return back to normal and should not be higher than 140/90. If high blood pressure is detected, your doctor should always repeat the reading to ensure its accuracy. Blood pressures that are on the borderline need to be followed very carefully to make certain they do not increase.
Some women start pregnancy with an existing high blood pressure problem called chronic hypertension. If you are one of these women, you should talk to your doctor about your blood pressure before you get pregnant, or, at the latest, during your first prenatal visit. Patients with chronic high blood pressure may benefit from blood pressure-lowering medicines before and throughout their pregnancies. Therefore, if you have chronic hypertension you should expect to be on medication for this problem during your pregnancy.
Often, a class of medicines called beta blockers or a drug called methyldopa is used in this scenario. It is important that you take the blood pressure-lowering medicines your doctor prescribes because in pregnancy, chronic hypertension can develop into more severe high blood pressure problems with serious consequences. For example, chronic hypertension is a predisposing factor for preeclampsia, and treatment of chronic hypertension can reduce the risk of developing preeclampsia.
One of the reasons blood pressure is monitored so carefully during pregnancy is to prevent a condition called preeclampsia, a type of hypertensive disorder that occurs during pregnancy.
Preeclampsia is classically defined by three problems:
Protein in the urine cannot be seen by the naked eye; your doctor must find it by laboratory analysis. Pregnant women may experience bloating during their pregnancies, but swelling is considered abnormal when it is generalized, involving the hands, face or legs.
Preeclampsia occurs in 5% to 30% of all pregnancies, depending on the population and the precise definition of the disease. It is unique to humans, and occurs after the 20th week of pregnancy. Preeclampsia is potentially a very dangerous condition that can cause: