Blood pressure is the force of the blood pushing against the walls of the arteries. Each time the heart beats, it pumps blood through the arteries. Your blood pressure is at its highest when the heart beats, forcing blood into the arteries. This is called systolic pressure. When the heart is at rest, between beats, your blood pressure falls. This is the diastolic pressure.

Blood pressure is always given as two numbers, the systolic and diastolic pressures. Both are important. The systolic pressure is the first or top number, and the diastolic pressure is the second or bottom number (for example, 120/80). If your blood pressure is 120/80, you say that it is "120 over 80".

Three out of four women in the western world have high blood pressure and know they have it. Yet fewer than one in three is controlling their blood pressure. Although many pregnant women with high blood pressure have healthy babies without serious problems, high blood pressure can be dangerous for both the mother and the fetus.

Women with pre-existing, or chronic, high blood pressure are more likely to have certain complications during pregnancy than those with normal blood pressure. However, some women develop high blood pressure while they are pregnant (often called gestational hypertension).The effects of high blood pressure during pregnancy can range from mild to severe.

High blood pressure can harm the mother's kidneys and other organs, and it can cause low birth weight and early delivery. In the most serious cases, the mother develops pre-eclampsia - or "toxaemia of pregnancy" - which can threaten the lives of both the mother and the fetus.

Pre-eclampsia is a condition that typically starts after the 20th week of pregnancy and is related to increased blood pressure and protein in the mother's urine (as a result of kidney problems). Pre-eclampsia affects the placenta, and it can affect the mother's kidney, liver, and brain. When pre-eclampsia causes seizures, the condition is known as eclampsia - and this is the second leading cause of maternal death in the western world.

Pre-eclampsia is also a leading cause of fetal complications, which include low birth weight, premature birth, and stillbirth. Women with one or more of the following conditions are most at risk for developing pre-eclampsia:

* Women with chronic hypertension (high blood pressure before becoming pregnant). * Women who developed high blood pressure or pre-eclampsia during a previous pregnancy, especially if these conditions occurred early in the pregnancy. * Women who are obese prior to pregnancy. Pregnant women under the age of 20 or over the age of 40. * Women who are pregnant with more than one baby. * Women with diabetes, kidney disease, rheumatoid arthritis, lupus, or scleroderma.

Women who develop signs of pre-eclampsia are closely monitored to lessen or avoid related problems. The only way to "cure" pre-eclampsia is to deliver the baby. High blood pressure problems occur in 6-8 percent of all pregnancies in the western world, about 70 percent of which are first-time pregnancies. To determine which life style changes and medications are appropriate, consult your doctor.