Tests and diagnosis

By Mayo Clinic Staff

Preeclampsia usually shows up during a routine prenatal blood pressure check followed by a urine test. The diagnosis depends on the presence of high blood pressure and protein in your urine after 20 weeks of pregnancy. Substances called biochemical markers in your blood and urine may be warning signs of preeclampsia. That's one of the reasons it's essential to seek early and regular prenatal care throughout your pregnancy.

A blood pressure reading in excess of 140/90 mm Hg is abnormal in pregnancy. However, a single high blood pressure reading doesn't mean you have preeclampsia. If you have one reading in the abnormal range — or a reading that's substantially higher than your usual blood pressure — your doctor will closely observe your numbers. Having a second abnormal blood pressure reading six hours after the first may confirm your doctor's suspicion of preeclampsia. You may also need additional blood pressure readings and urinary protein measurements.

Additional tests

If you're diagnosed with preeclampsia, your doctor may recommend additional tests, including:

  • Blood tests. These can determine how well your liver and kidneys are functioning and whether your blood has a normal number of platelets — the cells that help blood clot.
  • Prolonged urine collection test. Urine samples taken over at least 12 hours and up to 24 hours can quantify how much protein is being lost in the urine, an indication of the severity of preeclampsia.
  • Fetal ultrasound. Your doctor may also recommend close monitoring of your baby's growth, typically through ultrasound. This test directs high-frequency sound waves at the tissues in your abdominal area. These sound waves bounce off the curves and variations in your body, including your baby. The sound waves are translated into a pattern of light and dark areas — creating images of your baby on a monitor that can be recorded electronically or on film for a look at the inside of your uterus.
  • Nonstress test or biophysical profile. These make sure your baby is getting enough oxygen and nourishment. A nonstress test is a simple procedure that checks how your baby's heart rate reacts when your baby moves. Your baby is doing fine if the heart rate increases at least 15 beats a minute for at least 15 seconds twice in a 20-minute period. A biophysical profile combines an ultrasound with a nonstress test to provide more information about your baby's breathing, tone, movement and the volume of amniotic fluid in your uterus.
Apr. 21, 2011