Preeclampsia is a serious condition characterized by the new onset of high blood pressure, typically beginning after 20 weeks of gestation. This multi-system disorder can affect organ systems like the kidneys and liver. Consistent and early testing is important for prompt identification to safeguard the health of both the pregnant individual and the developing fetus. Testing for preeclampsia involves a continuous series of screenings and diagnostic evaluations.
Routine Screening Measures
The first indicators of potential preeclampsia are identified through simple, non-invasive tests performed at nearly every prenatal appointment. Systematic blood pressure measurement is a foundational screening tool that alerts healthcare providers to a developing problem. Hypertension is defined as a systolic reading of 140 millimeters of mercury (mmHg) or higher, or a diastolic reading of 90 mmHg or higher. These elevated readings must be confirmed on two occasions, separated by at least four hours.
Screening for protein in the urine, known as proteinuria, is the second routine measure performed with a simple urine dipstick test. The dipstick is a qualitative test, indicating only the presence or absence of protein, typically with a score of 1+ or greater suggesting a need for further investigation. The dipstick test is not precise enough to quantify the amount of protein loss or provide a definitive diagnosis. This initial screening acts as a filter, separating those requiring definitive laboratory testing from those without hypertensive complications.
Diagnostic Laboratory Tests
When routine screening indicates a problem, specific laboratory tests are ordered to confirm a preeclampsia diagnosis and assess the extent of organ involvement. Protein quantification is achieved through a 24-hour urine collection, which involves gathering all urine produced over a full day. The diagnosis of preeclampsia is confirmed if this collection totals 0.3 grams (300 mg) or more of protein. Alternatively, a spot urine sample can calculate a protein-to-creatinine ratio, with a value of 0.3 or higher being roughly equivalent to the 24-hour threshold.
Blood tests are performed to evaluate the function of the liver and kidneys, which are often affected by the disorder. Liver function tests (LFTs) measure enzymes like aspartate aminotransferase (AST) and alanine aminotransferase (ALT); levels that are double the normal concentration suggest impaired hepatic function. Kidney function is assessed by measuring serum creatinine, where a concentration of 1.1 mg/dL or a doubling of the baseline value indicates renal insufficiency. A complete blood count (CBC) is analyzed, with a platelet count below 100 x 10⁹/L indicating low platelets and disease severity.
Specialized Predictive Blood Tests
For individuals at high risk or when the diagnosis remains unclear, specialized blood tests measure specific biomarkers related to the disease’s underlying mechanism. Preeclampsia involves an imbalance of pro- and anti-angiogenic factors, which are proteins that regulate blood vessel growth. The key test measures the ratio between soluble fms-like tyrosine kinase-1 (sFlt-1) and Placental Growth Factor (PlGF).
PlGF promotes the development of new blood vessels, while sFlt-1 acts as an anti-angiogenic factor, neutralizing PlGF. In preeclampsia, sFlt-1 increases while PlGF decreases, resulting in a high sFlt-1/PlGF ratio that indicates widespread vascular dysfunction. This ratio serves as a powerful predictive tool, helping healthcare providers distinguish preeclampsia from other hypertensive disorders. A ratio of 38 or lower can effectively rule out the short-term onset of preeclampsia. Conversely, a ratio greater than 85 suggests a high likelihood of the disease’s presence or imminent development.
Monitoring Fetal Well-being
Since preeclampsia can restrict blood flow to the placenta, specialized tests are required to assess how the mother’s condition is impacting the developing fetus. The Non-Stress Test (NST) monitors the baby’s heart rate in response to its movements. A reassuring result, known as a “reactive” NST, shows appropriate accelerations in the heart rate, suggesting the baby is receiving adequate oxygen.
A more comprehensive evaluation is the Biophysical Profile (BPP), which combines the NST with an ultrasound to score five specific fetal parameters.
Fetal Parameters
- Body movement
- Muscle tone
- Breathing movements
- Heart rate reactivity
- Volume of amniotic fluid
Each component is scored, providing a clearer picture of the baby’s overall health status.
The Umbilical Artery Doppler uses ultrasound technology to measure the efficiency of blood flow through the umbilical cord between the mother and the fetus. Preeclampsia can increase resistance in the placental blood vessels, and the Doppler test detects this resistance by analyzing the blood flow patterns. An abnormal Doppler study is an early sign of placental insufficiency, prompting closer surveillance and informing decisions about the timing of delivery.