What are high blood pressure and preeclampsia?

Blood pressure is a measure of how hard your blood pushes against the walls of your arteries. If the force is too hard, you have high blood pressure (also called hypertension). When high blood pressure starts after 20 weeks of pregnancy, it may be a sign of a very serious problem called preeclampsia.

Blood pressure is shown as two numbers. The top number (systolic) is the pressure when the heart pumps blood. The bottom number (diastolic) is the pressure when the heart relaxes and fills with blood. Blood pressure is high if the top number is more than 140 millimeters of mercury (mm Hg), or if the bottom number is more than 90 mm Hg. For example, blood pressure of 150/85 (say "150 over 85") or 140/95 is high. Or both numbers can be high, such as 150/95.

A woman may have high blood pressure before she gets pregnant. Or her blood pressure may start to go up during pregnancy.

If you have high blood pressure during pregnancy, you need to have checkups more often than women who do not have this problem. There is no way to know if you will get preeclampsia. This is one of the reasons that you are watched closely during your pregnancy.

High blood pressure and preeclampsia are related, but they have some differences.

High blood pressure

Normally, a woman’s blood pressure drops during her second trimester. Then it returns to normal by the end of the pregnancy. But in some women, blood pressure goes up very high in the second or third trimester. This is sometimes called pregnancy-induced hypertension. It needs treatment, but it usually goes away after the baby is born.

High blood pressure that started before pregnancy usually doesn't go away after the baby is born.

A small rise in blood pressure may not be a problem. But your doctor will watch your pressure to make sure it does not get too high. The doctor also will check you for preeclampsia.

Very high blood pressure keeps your baby from getting enough blood and oxygen. This could limit your baby’s growth or cause the placenta to pull away too soon from the uterus. High blood pressure also could lead to stillbirth.

Preeclampsia

Preeclampsia is a pregnancy-related problem. The symptoms of preeclampsia include new high blood pressure after 20 weeks of pregnancy along with other problems, such as protein in your urine. Preeclampsia usually goes away after you give birth. In rare cases, blood pressure can stay high for up to 6 weeks after the birth.

Preeclampsia can be deadly for the mother and baby. It can keep the baby from getting enough blood and oxygen. It also can harm the mother’s liver, kidneys, and brain. Women with very bad preeclampsia can have dangerous seizures. This is called eclampsia.

What causes preeclampsia and high blood pressure during pregnancy?