What is high blood pressure? What is preeclampsia? How are they related?
When you have high blood pressure (hypertension), the force of blood against your artery walls is stronger than normal. If you have high blood pressure during a pregnancy, you must have more frequent checkups.
High blood pressure can remain mild during pregnancy, or it can become dangerously high and need treatment. It can also turn out to be a sign of preeclampsia, a pregnancy-related problem that can become life-threatening for you and/or your fetus.
High blood pressure
Normally, a pregnant woman's blood pressure drops during the second trimester and then returns to normal levels by the end of the third trimester. However, in 10% of pregnant women, blood pressure begins to increase to abnormally high levels in the second or third trimester.1 This is sometimes called pregnancy-induced hypertension.
- Mild high blood pressure during pregnancy is not necessarily dangerous by itself. However, it is closely monitored because it can be a sign of a more serious condition, such as preeclampsia. After delivery, mild high blood pressure that has not worsened during the pregnancy and has returned to normal within 12 weeks can be termed "transient hypertension of pregnancy."
- Severe high blood pressure limits the blood oxygen supply to your fetus, increasing the risk for poor fetal growth, early separation of the placenta from the uterine wall (placenta abruptio), and stillbirth. For this reason, you are likely to be treated with medication to lower your blood pressure if your diastolic blood pressure reading is 100 or higher (this is the second, or lower, number).
Long-term (chronic) high blood pressure is a lifelong yet treatable condition. The greatest risk for pregnant women with chronic high blood pressure is their 1-in-4 chance of developing preeclampsia.2 (When the two conditions occur together, your risk of complications from high blood pressure increases, as does your risk of complications from preeclampsia.)
Preeclampsia
Preeclampsia is defined as the new onset of high blood pressure over 140/90 millimeters of mercury (mm Hg) after 20 weeks of pregnancy, usually with higher-than-normal levels of protein found in a urine sample.
In its most severe form, preeclampsia is a life-threatening pregnancy problem. Although it is not well understood, preeclampsia seems to start with a placenta that doesn't grow the usual network of blood vessels deep into the uterine wall. This leads to poor blood circulation through the placenta.3 In addition to causing mild to severe high blood pressure, preeclampsia can also cause problems with blood supply to the fetus and sometimes with the woman's liver, kidney, and brain functions. Women with severe preeclampsia can develop life-threatening seizures (eclampsia).
Preeclampsia only occurs during or just after pregnancy. It affects about 5% of all pregnancies, most commonly first-time pregnancies.4 Although preeclampsia typically lasts for up to 2 weeks after delivery, it always goes away after a pregnancy.
Preeclampsia probably does not cause future high blood pressure. Instead, experts think that women who have preeclampsia also have a higher-than-normal risk of chronic high blood pressure after pregnancy or later in life.5
Both high blood pressure and preeclampsia can develop gradually or occur suddenly and can range from mild to severe. If you develop high blood pressure during pregnancy, there is no way of knowing whether it is a first sign of preeclampsia. This is why you are closely monitored for signs of preeclampsia throughout your pregnancy.
What causes high blood pressure during pregnancy? What causes preeclampsia?
Both preeclampsia and high blood pressure during pregnancy are caused by complex events in the body. Researchers are still studying these conditions.
Preeclampsia appears to have a genetic component. If your mother had preeclampsia while pregnant with you, you have an increased risk of developing preeclampsia during pregnancy. Similarly, if your partner in the pregnancy was born from a pregnancy affected by preeclampsia, your risk of developing preeclampsia is also higher than normal.
Experts also suspect that some women develop preeclampsia as a type of immune system reaction to the father's sperm, the placenta, or the fetus.6
Preeclampsia has been linked to placenta problems (such as a twin pregnancy with a larger placenta and poorer blood circulation than normal), high blood pressure, conditions that can lead to high blood pressure (such as obesity and polycystic ovary syndrome), and diabetes.5
What are the symptoms of high blood pressure and preeclampsia?
High blood pressure usually doesn't cause noticeable symptoms. However, severely high blood pressure sometimes causes headaches and shortness of breath or changes in vision.
Mild preeclampsia also doesn't typically cause noticeable symptoms. Preeclampsia can, however, cause rapid weight gain, problems with blood clotting, and sudden, persistent swelling of the hands and face. Severe preeclampsia causes signs of brain or organ trouble, including a severe headache, vision problems, breathing problems, abdominal pain, and decreased urination.
How are high blood pressure and preeclampsia diagnosed?
Because low-to-moderate high blood pressure and preeclampsia typically develop without causing symptoms, it is important to have a blood pressure check and a urine screen for higher-than-normal protein levels (a sign of preeclampsia) at each prenatal visit.
Your blood pressure is measured with a blood pressure cuff during every prenatal checkup. A sudden increase in blood pressure is typically the first sign of a possible problem.
Preeclampsia is diagnosed when blood pressure is 140/90 mm Hg. Many women also have increased levels of protein in their urine. However, if your blood pressure has recently gone up and you now have a headache or abdominal pain, tell your health professional right away. Preeclampsia can sometimes cause these signs and symptoms before protein shows up in a urine screen.3
How is high blood pressure treated during pregnancy? How is preeclampsia treated?
Mild-to-moderate long-term (chronic) high blood pressure during pregnancy is closely monitored, and blood pressure levels of 140/100 mm Hg and above may be treated with medication. Severe high blood pressure during pregnancy is typically treated with medication to prevent harm to the mother and fetus.
Depending on severity, preeclampsia may be treated with a medication to prevent seizures (eclampsia), blood pressure medication, or both.