Blood pressure is the force of the blood pushing against the artery walls. Each time the heart beats, it's pumping blood into these arteries. The highest blood pressure happens when the heart contracts and is pumping the blood. High blood pressure (hypertension) directly increases the risk of heart attack and stroke. Hypertension is defined in an adult as:

• Systolic pressure of 140 mm Hg or higher. Pressure is at its highest when the heart contracts and is pumping the blood. This is called systolic pressure.
• Diastolic pressure of 90 mm Hg or higher. When the heart is at rest between beats blood pressure falls. This is called diastolic pressure.

Chronic hypertension is when a pregnant person has pre-existing hypertension or develops it before 20 weeks of pregnancy.

Another form of hypertension in pregnancy is preeclampsia. Preeclampsia is a serious condition. It causes hypertension and problems with one or more organs, such as the kidneys. Chronic hypertension increases the risk for preeclampsia.

Most risks aren't increased for most people with mild chronic hypertension if there are no other complications. But risks are much greater for birth parent and baby if hypertension is severe. This is also true if there are other conditions, such as diabetes, or if preeclampsia develops along with chronic hypertension.

Risks of severe chronic hypertension in pregnancy may include:

• Blood pressure increasing
• Heart failure
• Bleeding in the brain
• Kidney failure
• Early detachment of the placenta from the uterus (placental abruption)

Risks to the baby before and after birth depend on how bad the disease is. The risks may include:

• Fetal growth restriction (less growth in the womb due to poor placental blood flow)
• Preterm birth (before 37 weeks of pregnancy)
• Stillbirth

It's important to have prenatal care with careful watching of blood pressure. Pregnant people with high blood pressure often need to keep taking their blood pressure medicine. Your doctor may switch you to a safer medicine while pregnant. A daily low dose aspirin (81 to 162 mg daily) may be advised to help prevent problems.

You may need tests on a regular basis. These are done to check the levels of substances in blood and urine related to hypertension. You may also need other tests to check your heart and kidney function. Testing of your baby may begin in the second trimester and may include:

• Ultrasound. Sound waves sent through a transducer are used to measure fetal growth.
• Nonstress test. This measures fetal heart rate in response to fetal movement.
• Biophysical profile. This is a test that combines an ultrasound with the nonstress test.
• Doppler flow studies. This is a type of ultrasound that uses sound waves to measure blood flow in babies with fetal growth restriction.