To diagnose preeclampsia, you have to have high blood pressure and one or more of the following complications after the 20th week of pregnancy:
- Protein in your urine (proteinuria)
- A low platelet count
- Impaired liver function
- Signs of kidney trouble other than protein in the urine
- Fluid in the lungs (pulmonary edema)
- New-onset headaches or visual disturbances
Previously, preeclampsia was only diagnosed if high blood pressure and protein in the urine were present. However, experts now know that it's possible to have preeclampsia, yet never have protein in the urine.
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 four hours after the first may confirm your doctor's suspicion of preeclampsia. Your doctor may have you come in for additional blood pressure readings and blood and urine tests.
Tests that may be needed
If your doctor suspects preeclampsia, you may need certain tests, including:
- Blood tests. Your doctor will order liver function tests, kidney function tests and also measure your platelets — the cells that help blood clot.
- Urine analysis. Your doctor will ask you to collect your urine for 24 hours, for measurement of the amount of protein in your urine. A single urine sample that measures the ratio of protein to creatinine — a chemical that's always present in the urine — also may be used to make the diagnosis.
- Fetal ultrasound. Your doctor may also recommend close monitoring of your baby's growth, typically through ultrasound. The images of your baby created during the ultrasound exam allow your doctor to estimate fetal weight and the amount of fluid in the uterus (amniotic fluid).
- Nonstress test or biophysical profile. A nonstress test is a simple procedure that checks how your baby's heart rate reacts when your baby moves. A biophysical profile uses an ultrasound to measure your baby's breathing, muscle tone, movement and the volume of amniotic fluid in your uterus.