Blood pressure is defined as the force of the blood against the arterial walls and it is reported using two numbers. The systolic pressure is the pressure recorded when the heart is actively pumping blood through the arteries. The diastolic pressure is the measurement taken when the heart is at rest between beats. The blood pressure measurement is given as the systolic pressure over the diastolic pressure.
According to MayoClinic.com, a normal blood pressure reading is below 120/80, although some doctors prefer to see readings lower than 115/ 75. Prehypertension occurs when the blood pressure reading is between 121/80 and 139/ 89. High blood pressure is defined as anything above 140/90. Low blood pressure occurs when the reading drops below 90/50. A diagnosis of high or low blood pressure can be made using either the systolic or diastolic reading if only one of the two measurements is outside of normal range.
During pregnancy, a woman experiences changes in blood pressure as a side effect of the increase in blood volume that occurs to support the developing baby. The most significant change in blood pressure is usually a drop in systolic pressure of five to 10 points and a drop in diastolic pressure of 10 to 15 points over the first 24 weeks of pregnancy, explains MayoClinic.com. According to the March of Dimes, about 8 percent of women experience high blood pressure during pregnancy instead of following the normal pattern of lower blood pressure.
If blood pressure gets too high during pregnancy, that can be a sign of preeclampsia, a dangerous condition that may cause seizures or death if left untreated. High blood pressure in pregnancy also raises the risk of preterm labor, fetal growth restriction and placental abruption. Low blood pressure during pregnancy may also be of concern, since this can result in dizziness. Also, a sudden drop in blood pressure of 20 points or more, even within normal ranges, can cause problems, including dizziness and fainting, and may even be deadly if the falling blood pressure cannot be stopped.
During pregnancy, blood pressure levels are an important indicator of potential problems, so the doctor typically takes a blood pressure reading at each prenatal visit. Home blood pressure monitors can be used between doctor's visits to keep track of blood pressure changes that might otherwise go unnoticed. Women who have high blood pressure before pregnancy, are at risk of preeclampsia or develop high blood pressure while pregnant are often advised to keep track of blood pressure at home.
Women who develop blood pressure outside of the normal range during pregnancy may receive a prescription for medication to control blood pressure. Some methods of maintaining blood pressure, such as limiting salt intake and embarking on a new exercise program, may not be appropriate for pregnant women. For women whose blood pressure goes far outside the normal range, a physician may recommend bed rest for the final weeks or months of pregnancy.