Preeclampsia is diagnosed largely from its symptoms. However, symptoms are not always apparent. The disorder is usually discovered during routine prenatal blood pressure checks and urine tests. As a result, regular prenatal care throughout a pregnancy is important for the diagnosis of preeclampsia.

High blood pressure (hypertension) is one of the primary signs of preeclampsia. Typically, blood pressure is measured by wrapping an arm cuff (attached to a monitor) snugly around the patient’s arm and then using a stethoscope to listen to the brachial artery located at the inside elbow on the same arm. The cuff is pumped full of air until circulation is briefly cut off. Then some air will be slowly let out of the device, loosening the cuff’s grip on the arm and allowing the blood to flow freely again. As the air is let out, the examiner watches the numbers coming down on a simple monitor (sphygmomanometer) and waits until first hearing the heartbeat. The number at which that occurs is the systolic pressure. The examiner remembers this as the numbers continue to come down on the monitor and notes the number at which the heartbeat is last heard. The number at which that occurs is the diastolic pressure.

However, a high blood pressure measurement is not enough to diagnose preeclampsia. A reading above the normal range, or a reading that is significantly higher than a woman’s normal blood pressure, will require close monitoring. The patient may be asked to visit the physician’s office for additional blood pressure checks and urine tests at least once a week and possibly more often.

The urine tests will be used to detect protein in the urine, another major sign of preeclampsia. For this test, a sample of the patient’s urine is collected. A chemically coated dipstick is then inserted into the urine to measure the amount of protein in the sample. Additionally, the patient may be asked to collect all of her urine over a 24 hour period of time to measure the total amount of protein in this specimen. When the patient has high blood pressure and proteinuria, blood tests may be ordered to verify the diagnosis.

The blood tests may focus on measuring the amount of platelets in the patient’s blood. Thrombocytopenia (a platelet count less than 100,000) is a sign of preeclampsia.

The obstetrician-gynecologist (ObGyn) may also order blood tests to detect hemolysis (destruction of red blood cells), and to determine if the liver is functioning normally. Elevated liver function test results and hemolysis are signs of the condition.

In addition, the physician may recommend using ultrasound (a device that uses sound waves to produce an image of the uterus) to monitor the fetus’ growth. The patient may also require a nonstress test (NST) or biophysical profile. These tests can be used to determine if the fetus is getting enough oxygen and nourishment. An NST is a non-invasive test that measures how often the fetus moves and how much its heart rate increases with each movement. A biophysical profile is a test that combines an ultrasound with an NST to reveal information about the fetus’s breathing, movement and tone. It also provides information about the amount of amniotic fluid in the mother’s uterus.