Introduction
Preeclampsia is the most common serious medical disorder of human pregnancy.
The definition of preeclampsia involves a collection of clinical features usually appearing at or after 20 weeks of pregnancy. These are the development of high blood pressure (BP ≥140/90), accompanied by at least one of the following new-onset conditions:
• excessive protein in the urine,
• liver, nervous system, blood, and other organ and tissue abnormalities,
• and/or poor placental function leading to fetal growth restriction.
A major historical justification for undertaking antenatal care (and one which remains relevant today) has been screening for preeclampsia by measuring blood pressure at routine clinical visits. This approach facilitates the eventual diagnosis of preeclampsia but does not lend itself to predicting or preventing the condition.
Recent advances in early pregnancy screening technology and the discovery of circulating placental factors later in pregnancy that are associated with preeclampsia now offer opportunities to correct this shortcoming and allow a major pregnancy care recalibration in favour of preeclampsia prediction (and thus prevention) rather than diagnosis.
These new preeclampsia prediction tests are not yet widely available in Australia.
However, AAPEC is supporting initiatives to have these tests reimbursed through Medicare which will make them more easily available to all pregnant women in Australia.
Early Pregnancy Prediction Test
Early screening from 11–14 weeks of pregnancy using a combined calculation involving a careful check of maternal blood pressure, an ultrasound-based assessment of blood flow to the uterus, a blood sample to measure a protein called placental growth factor, and information regarding maternal medical history, allows for significantly better early detection of pregnant women at increased risk of later pregnancy preeclampsia than relying on maternal medical history assessment alone, though such clinical assessment is helpful in the selection of cases for such early screening.
Importantly, this early identification of women considered to be at high risk of developing preeclampsia allows them to receive prophylaxis with low dose aspirin (eg 150 mg daily, taken at night) in a sufficiently timely fashion to significantly reduce their risk of disease, particularly early-onset and preterm preeclampsia.
Later Pregnancy Prediction Test
The placental circulating factors that form the basis of this test are:
• soluble fms-like tyrosine kinase 1 (sFlt-1) (which increases in the maternal bloodstream in advance of the clinical appearance of preeclampsia), and
• placental growth factor (PlGF) (which decreases in the maternal bloodstream in advance of the clinical appearance of preeclampsia).
These molecules can be measured in blood samples in clinical pathology laboratories and are usually reported as a ratio of sFlt-1/PlGF (herein called the PreEclampsia RaTio or PERT test).
An increasing number of clinical research studies in Australia and overseas are demonstrating the clinical utility of the PERT test in the latter half of pregnancy for the prediction, diagnosis, and management of preeclampsia.
In particular, the PERT test has been shown to assist cost-effective decision-making regarding appropriate hospitalization in women with suspected preeclampsia. Using this test, a low-risk result means a woman can safely continue with routine outpatient antenatal care at least for several weeks, whereas a high-risk result supports a need for increased maternal and fetal welfare surveillance, possibly as an inpatient. Such stratification optimises patient satisfaction and cost-effective use of hospital resources.
Conclusion
These new tests for identifying women at risk of developing preeclampsia promise to significantly improve pregnancy outcomes for mothers and their babies. Just as importantly, these tests will also allow women identified as low risk to safely minimize unnecessary interventions during their pregnancies.
Further information
Click here to watch our 2021 World Preeclampsia Day Webinar.
Click here to read the journal article on “Clinical interpretation and implementation of the sFlt-1/PlGF ratio in the prediction, diagnosis, and management of preeclampsia”.