1T Pre-Term Preeclampsia Screen

Risk Calculation: 
Each marker level is converted into a multiple of the GA specific median (MoM) and is then adjusted as applicable based on the patient's race, weight, diabetic status, multiple pregnancy status, Egg Donor status, and smoking status.  Patient specific risks for pre-term preeclampsia are calculated following the competing risks approach developed by the Fetal Medicine Foundation (FMF) using Bayes theorem to combine the a priori risk from maternal characteristics and medical history with the results of the  biophysical and biochemical measurements.   This approach assumes that if the pregnancy was to continue indefinitely all women would eventually develop PE and whether they do so or not depends on competition between which comes first, delivery or the development of PE. This approach allows the estimation of the individual patient-specific risks of delivery with preeclampsia before 37 weeks gestational age. 

An interpretive risk report including the patient's marker levels, cut-off values and risk for pre-term preeclampsia will be provided.

Pre-Term Preeclampsia Interpretation:
The risk cut-off is set equal to 1/150.  This test may detect over 80% of cases destined to develop preeclampsia necessitating delivery prior to 37 weeks gestational age including over 90% of cases <34 weeks at an approximate 15% false positive rate.

Since the prior risk of twins is high, most twins will screen positive. Comparison of the after screening risk to the before screening risk may be of assistance in evaluating the pregnancy.

Test Follow Up: 
If the patient's risk is less than the cut-off risk the test is considered "Within Normal Range" and no further action is required. If the patient’s risk is greater than or equal to the cut-off risk the test is considered "Increased Risk". 

Patients at increased risk may be offered: 
1.    Education regarding the signs and symptoms of preeclampsia
2.    Increased monitoring including the option of home blood pressure monitoring
3.    Prophylactic low-dose aspirin starting prior to 16 weeks to reduce the risk of preeclampsia, IUGR and Preterm Delivery.

Upon receiving pre-term preeclampsia screening results, all information used in the risk calculation should be reviewed for accuracy (i.e., weight, diabetic status, gestational dating). If any information is incorrect, the laboratory should be contacted for recalculation of the estimated risks. ‘Within Range’ risk results typically do not warrant further evaluation. The screen results are dependent on accurate demographic information.  Inaccurate information can lead to significant alterations in the estimated risk. In particular, erroneous assessment of gestational age can result in false-positive or false-negative screen results. 

Disclaimers
This is a screening test, not a diagnostic test. A ‘Within Range’ risk result indicates low risk for the conditions screened but does not guarantee the absence of those conditions or other abnormalities. An ‘Increased Risk’ result indicates an increased risk for the condition screened but does not infer a definitive diagnosis. 

Cautions
Valid measurements of maternal serum markers cannot be made after CVS or amniocentesis. Triplets and higher order multiple pregnancies cannot be interpreted. In rare cases, some individuals can develop antibodies to mouse or other animal antibodies (often referred to as human anti-mouse antibodies [HAMA] or heterophile antibodies), which may cause interference in some immunoassays. Caution should be used in interpretation of results and the laboratory should be alerted if the result does not correlate with the clinical presentation.

Each center offering pre-term preeclampsia screening to patients should establish a standard screening protocol, which provides pre- and post-screening education and appropriate follow-up for ‘Increased Risk’ results.

Clinical References 
(1)  Rolnik DL, Wright D, Poon LC, et al. Aspirin versus placebo in pregnancies at high risk for preterm preeclampsia. N Engl J Med 2017;377: 613–22.\
(2)  Akolekar R, Syngelaki A, Poon L, Wright D, Nicolaides KH. Competing risks model in early screening for preeclampsia by biophysical and biochemical markers. Fetal Diagn Ther 2013;33: 8–15.
(3)  Rolnik DL, Wright D, Poon LCY, et al.  ASPRE trial: performance of screening for pre-term pre-eclampsia. Ultrasound Obstet Gynecol 2017;50:492–5.
(4)  Chaemsaithong P, Sahota DS, Poon LC.  First trimester preeclampsia screening and
prediction. Am J Obstet Gynecol. 2022 Feb;226(2S):S1071-S1097.e2.
(5)  Foster AB, Park, F, Hyett J.  Do first‐trimester screening algorithms for preeclampsia aligned to use of preventative therapies reduce the prevalence of pre‐term preeclampsia: A systematic review and meta‐analysis.  Prenatal Diagnosis. 2023;43:950–958.