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Chronic hypertension refers to high blood pressure that is diagnosed in women before pregnancy or before the 20th week of pregnancy. Some physicians also use the phrase to describe high blood pressure that presents for the first time during late pregnancy but persists for several weeks after delivery. High blood pressure is defined as a range of the arterial pressure that exceeds 120 millimeters of mercury at its highest level or 90 millimeters of mercury at its lowest level. Chronic hypertension can increase the risks of pregnancy for both the three percent of mothers who have it and their fetuses. Close physician monitoring and proper prenatal care, however, allows most mothers with chronic hypertension to deliver their babies safely.
Throughout pregnancy, the blood volume increases by 40 to 50 percent. The cardiac output increases by about the same amount. This, along with other factors, can lead to congestive heart failure. Heart problems complicate one to four percent of pregnancies in women without a known history of heart abnormalities.
Other health complications accompanying chronic hypertension include kidney failure, liver problems, clotting disorders, and brain hemorrhages. Abruptio placenta, a particularly life-threatening condition, refers to an early separation of the placenta from the uterus wall, leading to excessive bleeding and shock. Signs of placental abruption also include abdominal pain and rigidity. Disruption of the blood flow through the placenta to the baby can cause fetal distress.
Maternal hypertension also poses risks to the developing baby, including premature birth and stillbirth. Delayed fetal growth with low birth weight results from inadequate blood flow to the placenta, a condition called intrauterine growth retardation. Clinical studies reveal that lowering maternal blood pressure with medications and daily administration of low-dose aspirin significantly increase the growth rate in babies of mothers with chronic hypertension. The low-dose aspirin enhances the uterus and placental blood flow.
Sometimes confused with chronic hypertension, preeclampsia is a medical condition characterized by increased blood pressure and kidney dysfunction, indicated by increased protein in the mother's urine. Preeclampsia begins after the 20th gestational week. The Hypertension-Elevated Liver Enzymes-Low Platelets (HELLP) syndrome can accompany preeclampsia. HELLP syndrome can indicate damage to the maternal liver, kidney, and brain. Physicians infuse magnesium citrate to prevent seizures, the leading cause of death in pregnant women. Doctors treat mothers with preeclampsia by delivering the baby.