Monitoring blood pressure during pregnancy is important because the blood pressure affects both the mother and the fetus. The average normal blood pressure in pregnancy is about 120/80 millimeters of mercury (mm Hg), although numerous factors can alter blood pressure readings. While some women can have higher blood pressure without experiencing any side effects, dangerously high blood pressure can cause potentially serious complications. Maintaining a normal blood pressure in pregnancy can help reduce the risk of complications.
Blood pressure readings measure the amount of force the blood exerts against the walls of the arteries. A nurse or physician uses a blood pressure cuff or automatic cuff to measure the force of the blood. A reading is considered high when the top number, or the systolic pressure, is greater than 140 mm Hg), or the bottom number, the diastolic pressure, is greater than 90 mm Hg.
Several factors can affect the rate of normal blood pressure in pregnancy. Some people tend to get anxious around doctors, leading to what is commonly referred to as “white coat syndrome.” The mere presence of a doctor or nurse can cause blood pressure to rise. Exercising before taking a blood pressure test can also cause an inaccurate reading. Blood pressure taken in one arm can also be different from pressure taken in the other.
Normal blood pressure in pregnancy is typically lower during the first two trimesters than in the last trimester. Progesterone, a hormone that helps support the pregnancy, relaxes the vessels of the body, allowing blood to flow more freely. Plasma production in the blood doubles, diluting the overall volume. During the third trimester, the capacity of the vessels returns to normal and the extra blood volume causes a slight increase in blood pressure.
Abnormally high blood pressure in pregnancy can lead to a condition called preeclampsia. The condition typically begins after the 20th week of pregnancy and can affect the mother’s liver, kidneys and brain. Preeclampsia is one of the leading causes of low birth weight, premature birth and stillbirth. The condition is unpredictable, cannot be prevented, and can only be cured by delivering the baby.
In addition to hypertension, other signs of preeclampsia include protein in the mother's urine, swelling throughout the body, blurred vision, and headaches. If preeclampsia progresses unchecked, it can lead to a life-threatening condition called eclampsia, which causes seizures and can sometimes death. Intravenous magnesium sulfate therapy can help prevent serious complications.
Women can help maintain a normal blood pressure in pregnancy by exercising, reducing salt intake, and staying away from tobacco or alcohol. In many cases, however, preeclampsia is not preventable. Regular blood pressure monitoring and proper prenatal care is vital to ensuring both the woman’s and the fetus’ continued health.
