Predictive value of the soluble fms-like tyrosine kinase 1 to placental growth factor ratio for preeclampsia in twin pregnancies: a systematic review and meta-analysis

OBJECTIVE

In recent years, the ratio of soluble fms-like tyrosine kinase 1 to placental growth factor for use in predicting preeclampsia has been explored extensively. Despite extensive research, available data on its effectiveness in predicting preeclampsia in twin pregnancies are limited and conflicting. This meta-analysis aimed to assess the diagnostic accuracy of the soluble fms-like tyrosine kinase 1 to placental growth factor ratio in distinguishing cases with preeclampsia in twin pregnancies from healthy controls.

DATA SOURCES

Studies that evaluated the use of the soluble fms-like tyrosine kinase 1 to placental growth factor ratio in predicting preeclampsia were searched in PubMed, Embase, and Cochrane databases from inception to August 6, 2023, without language restriction.

STUDY ELIGIBILITY CRITERIA

The following population, exposure, comparators, outcomes, and study designs were included: women with twin pregnancies; an increased soluble fms-like tyrosine kinase 1 to placental growth factor ratio with preeclampsia as the outcome; women without preeclampsia; a 2 × 2 diagnostic table, diagnostic accuracy data, and the incidence of preeclampsia; and prospective cohort studies and observational comparative studies, respectively.

STUDY APPRAISAL AND SYNTHESIS METHODS

The quality of the included studies was evaluated. Key parameters, including the specificity, sensitivity, positive likelihood ratio, negative likelihood ratio, and diagnostic odds ratio, were calculated using the random- and fixed-effects models. In addition, the area under the receiver operating characteristic curve and the summary receiver operating characteristic curve were evaluated.

RESULTS

A total of 7 studies were included, including 442 women with twin pregnancies (115 patients with preeclampsia and 327 controls without preeclampsia). The results highlighted the promising effectiveness of the soluble fms-like tyrosine kinase 1 to placental growth factor ratio in predicting preeclampsia in twin pregnancies with a pooled specificity of 0.89 (95% confidence interval, 0.80-0.95), a sensitivity of 0.84 (95% confidence interval, 0.73-0.93), a positive likelihood ratio of 32.76 (95% confidence interval, 12.82-83.74), and a negative likelihood ratio of 0.03 (95% confidence interval, 0.01-0.08). The combined diagnostic odds ratio was 35.72 (95% confidence interval, 12.92-98.76), and the area under the receiver operating characteristic curve was 0.92.

CONCLUSION

These collective findings underscore the potential of the soluble fms-like tyrosine kinase 1 to placental growth factor ratio as an accurate marker for identifying preeclampsia among women with twin pregnancies.

[Preeclampsia: Guidelines for clinical practice from the French College of Obstetricians and Gynecologists]

OBJECTIVE

To identify strategies to reduce maternal and neonatal morbidity related to preeclampsia.

MATERIAL AND METHODS

The quality of evidence of the literature was assessed following the GRADE® method with questions formulated in the PICO format (Patients, Intervention, Comparison, Outcome) and outcomes defined a priori and classified according to their importance. An extensive bibliographic search was performed on PubMed, Cochrane, EMBASE and Google Scholar databases. The quality of the evidence was assessed (high, moderate, low, very low) and recommendations were formulated as a (i) strong, (ii) weak or (iii) no recommendation. The recommendations were reviewed in two rounds with external reviewers (Delphi survey) to select the consensus recommendations.

RESULTS

Preeclampsia is defined by the association of gestational hypertension (systolic blood pressure≥140mmHg and/or diastolic blood pressure≥90mmHg) and proteinuria≥0.3g/24h or a Proteinuria/Creatininuria ratio≥30mg/mmol occurring after 20 weeks of gestation. Data from the literature do not show any benefit in terms of maternal or perinatal health from implementing a broader definition of preeclampsia. Of the 31 questions, there was agreement between the working group and the external reviewers on 31 (100%). In general population, physical activity during pregnancy should be encouraged to reduce the risk of preeclampsia (Strong recommendation, Quality of the evidence low) but an early screening based on algorithms (Weak recommendation, Quality of the evidence low) or aspirin administration (Weak recommendation, Quality of the evidence very low) is not recommended to reduce maternal and neonatal morbidity related to preeclampsia. In women with preexisting diabetes or hypertension or renal disease, or multiple pregnancy, the level of evidence is insufficient to determine whether aspirin administration during pregnancy is useful to reduce maternal and perinatal morbidity (No recommendation, Quality of the evidence low). In women with a history of vasculo-placental disease, low dose of aspirin (Strong recommendation, Quality of the evidence moderate) at a dosage of 100-160mg per day (Weak recommendation, Quality of the evidence low), ideally before 16 weeks of gestation and not after 20 weeks of gestation (Strong recommendation, Quality of the evidence low) until 36 weeks of gestation (Weak recommendation, Quality of the evidence very low) is recommended. In a high-risk population, additional administration of low molecular weight heparin is not recommended (Weak recommendation, Quality of the evidence moderate). In case of preeclampsia (Weak recommendation, Quality of the evidence low) or suspicion of preeclampsia (Weak recommendation, Quality of the evidence moderate, the assessment of PlGF concentration or sFLT-1/PlGF ratio is not routinely recommended) in the only goal to reduce maternal or perinatal morbidity. In women with non-severe preeclampsia antihypertensive agent should be administered orally when the systolic blood pressure is measured between 140 and 159mmHg or diastolic blood pressure is measured between 90 and 109mmHg (Weak recommendation, Quality of the evidence low). In women with non-severe preeclampsia, delivery between 34 and 36+6 weeks of gestation reduces severe maternal hypertension but increases the incidence of moderate prematurity. Taking into account the benefit/risk balance for the mother and the child, it is recommended not to systematically induce birth in women with non-severe preeclampsia between 34 and 36+6 weeks of gestation (Strong recommendation, Quality of evidence high). In women with non-severe preeclampsia diagnosed between 37+0 and 41 weeks of gestation, it is recommended to induce birth to reduce maternal morbidity (Strong recommendation, Low quality of evidence), and to perform a trial of labor in the absence of contraindication (Strong recommendation, Very low quality of evidence). In women with a history of preeclampsia, screening maternal thrombophilia is not recommended (Strong recommendation, Quality of the evidence moderate). Because women with a history of a preeclampsia have an increased lifelong risk of chronic hypertension and cardiovascular complications, they should be informed of the need for medical follow-up to monitor blood pressure and to manage other possible cardiovascular risk factors (Strong recommendation, Quality of the evidence moderate).

CONCLUSION

The purpose of these recommendations was to reassess the definition of preeclampsia, and to determine the strategies to reduce maternal and perinatal morbidity related to preeclampsia, during pregnancy but also after childbirth. They aim to help health professionals in their daily clinical practice to inform or care for patients who have had or have preeclampsia. Synthetic information documents are also offered for professionals and patients.

Advances in preeclampsia testing

Preeclampsia is a multisystem hypertensive disorder and one of the leading causes of maternal and fetal morbidity and mortality. The clinical hallmarks such as hypertension and proteinuria, and additional laboratory tests currently available including liver enzyme testing, are neither specific nor sufficiently sensitive. Therefore, biomarkers for timely and accurate identification of patients at risk of developing preeclampsia are extremely valuable to improve patient outcomes and safety. In this chapter, we will first discuss the clinical characteristics of preeclampsia and current evidence of the role of angiogenic factors, such as placental growth factor (PlGF) and soluble FMS like tyrosine kinase 1 (sFlt-1) in the pathogenesis of preeclampsia. Second, we will review the clinical practice guidelines for preeclampsia diagnostic criteria and their recommendations on laboratory testing. Third, we will review the currently available PlGF and sFlt-1 assays in terms of their methodologies, analytical performance, and clinical diagnostic values. Finally, we will discuss the future research needs from both an analytical and clinical perspective.

Comparison of the Soluble fms-Like Tyrosine Kinase 1/Placental Growth Factor Ratio Alone versus a Multi-Marker Regression Model for the Prediction of Preeclampsia-Related Adverse Outcomes after 34 Weeks of Gestation

INTRODUCTION

The objective of this retrospective study was to compare the predictive performance of the soluble fms-like tyrosine kinase 1 (sFlt-1)/placental growth factor (PlGF) ratio alone or in a multi-marker regression model for preeclampsia-related maternal and/or fetal adverse outcomes in women >34 weeks of gestation.

METHODS

We analyzed the data collected from 655 women with suspected preeclampsia. Adverse outcomes were predicted by multivariable and univariable logistic regression models. The outcome of patients was evaluated within 14 days after presentation with signs and symptoms of preeclampsia or diagnosed preeclampsia.

RESULTS

The full model integrating available, standard clinical information and the sFlt-1/PlGF ratio had the best predictive performance for adverse outcomes with an AUC of 72.6%, which corresponds to a sensitivity of 73.3% and specificity of 66.0%. The positive predictive value of the full model was 51.4%, and the negative predictive value was 83.5%. 24.5% of patients, who did not experience adverse outcomes but were classified as high risk by sFlt-1/PlGF ratio (≥38), were correctly classified by the regression model. The sFlt-1/PlGF ratio alone had a significantly lower AUC of 65.6%.

CONCLUSIONS

Integrating angiogenic biomarkers in a regression model improved the prediction of preeclampsia-related adverse outcomes in women at risk after 34 weeks of gestation.

Analytical Performance and Quality Indicators of Fully Automated Immunoassays for sFlt-1 and PlGF

BACKGROUND

The ratio of the antiangiogenic factor, soluble fms-like tyrosine kinase 1 (sFlt-1), to the proangiogenic factor, placental growth factor (PlGF), is associated with increased risk of preeclampsia. Here, we describe an analytical evaluation of the Elecsys sFlt-1 and PlGF assays at the first North American site in which they were clinically implemented.

METHODS

The analytical evaluation included short- and long-term imprecision, method comparison, accuracy, linearity, sample stability, limit of quantification verification, and measurement uncertainty. Quality indicators were also evaluated, including turnaround time and repeat test frequency.

RESULTS

Short-term (13-day) and long-term (12-month) imprecision for sFlt-1 and PlGF were <4% CV. Method comparison (n = 40) between Roche cobas e602 and e411 exhibited r > 0.99 and bias <10%. sFlt-1/PlGF ratio rule-out cutoffs (≤33 and ≤38) and rule-in cutoffs (>38, >85, and >110) exhibited negative percent agreement and positive percent agreement of 100%, respectively (n = 40). During the first 12 months, 257 orders were placed, repeat test frequency was 17.5%, mean time between repeat orders was 23 days, and 72.0% of results were reported within 2 h from sample receipt when quality control was run continuously.

CONCLUSIONS

We describe analytical performance parameters and quality indicators of the Elecsys sFlt-1 and PlGF assays, which was the first North American clinical laboratory site to implement these assays in support of the institution's high-risk obstetrical unit.

The diagnostic value of angiogenic and antiangiogenic factors in differential diagnosis of preeclampsia

The definition of preeclampsia is changing. However, with the addition of organ symptoms to the presence of hypertension in pregnancy instead of relying only on proteinuria, a more precise detection of women at risk of preeclampsia-associated adverse events has not been achieved. Instead, under the new definitions of the American College of Obstetricians and Gynecologists and of the International Society for the Study of Hypertension in Pregnancy, more women are classified as preeclamptic, with a tendency to milder disease. Furthermore, angiogenic and antiangiogenic factors have emerged as essential tools for predicting and diagnosing preeclampsia at high accuracies. Next to being rooted in the pathophysiology of the disease, they have been proven to be reliable tools for predicting and diagnosing the disease. In addition, 2 cutoffs have been evaluated for the clinical setting. As shown in the Prediction of Short-Term Outcome in Pregnant Women With Suspected Preeclampsia Study, at the soluble fms-like tyrosine kinase-1-to-placental growth factor ratio cutoff of 38, a preeclampsia can be ruled out for 1 week with a negative predictive value of 99.3% (95% confidence interval, 97.9-99.9) and ruled in with a positive predictive value of 36.7% (95% confidence interval, 28.4-45.7). The diagnostic cutoff of 85 has been shown to accurately identify women with preeclampsia, with a sensitivity of up to 88% and a specificity of 99.5%. In this review, we highlight the central role of angiogenic and antiangiogenic factors in the differential diagnosis of women presenting at high risk of the disease, such as patients with chronic hypertension or chronic kidney disease. We will focus on their ability to predict preeclampsia-associated adverse fetal and maternal outcomes. This is only possible when critically reviewing the evolution of the definition of "preeclampsia." We show how changes in this definition shape our clinical picture of the condition and how angiogenic and antiangiogenic biomarkers might be included to better identify women destined to develop preeclampsia-related adverse outcomes.

Serum Biomarkers of Maternal Morbidity and Adverse Outcome in Severe Pre-Eclampsia

OBJECTIVE

To evaluate the association of maternal serum biomarkers of myocardial damage, oxidative stress and angiogenic imbalance with maternal adverse outcomes in women with severe pre-eclampsia.

METHODS

This was a prospective cohort study, where maternal serum biomarkers were evaluated in women admitted with severe pre-eclampsia to a tertiary care centre between March 2019 and February 2020. Serum markers included brain naturetic peptide (BNP), cardiac troponin-T (cTnT), cystatin-C (cys-C), soluble fms-like tyrosine kinase-1 (sFlt-1), placental growth factor (PlGF), Total Anti-Oxidant status (TAO) and malondialdehyde (MAO). Main outcome measures were adverse maternal outcomes defined as eclampsia, pulmonary oedema, acute kidney injury, placental abruption and HELLP syndrome.

RESULTS

Adverse maternal outcomes occurred in 93(37.2%, 95% CI: 31.2%-43.6%) of the 250 women with severe pre-eclampsia included in the study, including 21 with pulmonary oedema, 25 with acute kidney injury and 36 with eclampsia. BNP levels were higher among women who developed pulmonary oedema (55.4 pg/mL vs 42.0 pg/mL, p = 0.008). TAO levels were higher in women who developed eclampsia (4.6 mM, IQR 3.1-5.7, p < 0.001) and acute kidney injury (4.1 mM, IQR 3.2-6.3, p = 0.002) compared to those who did not develop any complications (2.93 mM, IQR 2.3-4.1).

CONCLUSIONS

Even though the endothelial dysfunction and oxidative stress biomarkers were associated with development of preeclampsia, it may have limited utility in identifying women who might develop adverse outcomes.

Prospective evaluation of first-trimester screening strategy for preterm pre-eclampsia and its clinical applicability in China

OBJECTIVES

To evaluate, in a Chinese population, the performance of a screening strategy for preterm pre-eclampsia (PE) using The Fetal Medicine Foundation (FMF)'s competing-risks model and to explore its clinical applicability in mainland China.

METHODS

This was a prospective, multicenter, observational cohort study including 10 899 women with singleton pregnancy who sought prenatal care at one of 13 hospitals, located in seven cities in mainland China, between 1 December 2017 and 30 December 2019. Mean arterial pressure (MAP), uterine artery pulsatility index (UtA-PI) and maternal serum levels of placental growth factor (PlGF) and pregnancy-associated plasma protein-A (PAPP-A) at 11 + 0 to 13 + 6 weeks' gestation were measured and converted into multiples of the median using Chinese reference ranges. Individualized risk for preterm PE was calculated using the FMF algorithm. Prior risk was calculated based on maternal demographic characteristics and obstetric history. We evaluated the efficiency of the screening strategy using various combinations of biomarkers and analyzed its predictive performance for a composite of placenta-associated adverse pregnancy outcomes, including PE, placental abruption, small-for-gestational age (SGA) and preterm birth, at fixed false-positive rates for preterm PE.

RESULTS

We identified 312 pregnancies that developed PE, of which 117 cases were diagnosed as preterm PE (< 37 weeks' gestation). There were 386 pregnancies complicated by severe composite placenta-associated adverse outcome, including preterm PE, 146 cases of severe SGA (birth weight < 3^rd percentile) neonate, 61 cases with placental abruption and 109 cases of early preterm birth < 34 gestational weeks. The triple-marker model containing biomarkers MAP, UtA-PI and PAPP-A achieved, at fixed false-positive rates of 10%, 15% and 20%, detection rates for preterm PE of 65.0%, 72.7% and 76.1%, respectively, and detection rates for severe composite placenta-associated adverse outcome of 34.7%, 41.7% and 46.4%, respectively. Replacing PAPP-A with PlGF or adding PlGF to the model did not improve the performance. Of women screening positive for preterm PE at a fixed 5% false-positive rate, an estimated 30% developed at least one placenta-associated adverse pregnancy outcome, including PE, placental abruption, SGA (birth weight < 10^th percentile) and preterm birth < 37 weeks.

CONCLUSIONS

The FMF competing-risks model for preterm PE was found to be effective in screening a mainland Chinese population. Women who screened positive for preterm PE had increased risk for other placenta-associated pregnancy complications. © 2021 International Society of Ultrasound in Obstetrics and Gynecology.

Short-Term Prediction of Preeclampsia in Chinese Women Using the Soluble fms-Like Tyrosine Kinase 1/Placental Growth Factor Ratio: A Sub-Analysis of the PROGNOSIS Asia Study

The diagnosis of preeclampsia in China currently relies on limited clinical signs and unspecific laboratory findings. These are inadequate predictors of preeclampsia development, limiting early diagnosis and appropriate management. Previously, the Prediction of Short-Term Outcome in Pregnant Women with Suspected Preeclampsia Study (PROGNOSIS) and PROGNOSIS Asia demonstrated that a soluble fms-like tyrosine kinase 1 (sFlt-1)/placental growth factor (PlGF) ratio of ≤38 can be used to rule out preeclampsia within 1 week, with negative predictive values of 99.3 and 98.6%, respectively. This is an exploratory sub-analysis of the Chinese cohort (n = 225) of the PROGNOSIS Asia study. The primary objectives were to assess the predictive performance of using the sFlt-1/PlGF ratio to rule out preeclampsia within 1 week and to rule in preeclampsia within 4 weeks. The sFlt-1/PlGF ratio was also examined for short-term prediction of fetal adverse outcomes, maternal adverse outcomes, and time to delivery. The overall prevalence of preeclampsia was 17.3%. With the use of an sFlt-1/PlGF ratio of ≤38, the negative predictive value for ruling out preeclampsia within 1 week was 97.3% [95% confidence interval (CI), 93.8-99.1], with a sensitivity of 64.3% and specificity of 85.3%. With the use of an sFlt-1/PlGF ratio of >38, the positive predictive value for ruling in preeclampsia within 4 weeks was 35.0% (95% CI, 20.6-51.7), with a sensitivity of 50.0% and specificity of 86.8%. In the analyses of the sFlt-1/PlGF ratio and fetal adverse outcomes, the area under the receiver operating characteristic curve was 92.8% (95% CI, 83.5-98.7) for ruling out fetal adverse outcomes within 1 week and 79.9% (95% CI, 68.1-90.3) for ruling in fetal adverse outcomes within 4 weeks. An sFlt-1/PlGF ratio of >38 increased the likelihood of imminent delivery 3.3-fold compared with a ratio of ≤38 [hazard ratio, 3.3 (95% CI, 2.1-5.1)]. This sub-analysis confirms the high predictive performance of the sFlt-1/PlGF ratio cutoff of 38 for short-term prediction of preeclampsia in Chinese women, which may help prevent unnecessary hospitalization of women with low risk of developing preeclampsia.

Decision Threshold for Kryptor sFlt-1/PlGF Ratio in Women With Suspected Preeclampsia: Retrospective Study in a Routine Clinical Setting

Background The objective was to evaluate predictive performance and optimal decision threshold of the Kryptor soluble fms-like tyrosine kinase-1 (sFlt-1)/placental growth factor (PlGF) ratio when implemented for routine management of women presenting with symptoms of preeclampsia. Methods and Results Observational retrospective study of a cohort of 501 women with suspected preeclampsia after 20 weeks of gestation. Women referred to maternity ward for observation of preeclampsia had an sFlt-1/PlGF ratio test included in routine diagnostic workup. Maternal and offspring characteristic data included maternal risk factors, outcomes, delivery mode, and indication for suspected preeclampsia. Biochemical measurements to determine sFlt-1/PlGF ratio were performed using the BRAHMS/Kryptor sFlt-1/PlGF ratio immunoassays. Results were analyzed by area under receiver-operating characteristic curve. Preeclampsia occurred in 150 of 501 (30%) of symptomatic women with an sFlt-1/PlGF ratio determined before the time of diagnosis. Area under receiver-operating characteristic curve for diagnosis of early-onset preeclampsia within 1 and 4 weeks was 0.98 (95% CI, 0.96-1.00) and 0.95 (95% CI, 0.92-0.98), respectively. For late-onset preeclampsia, predictive performance within 1 and 4 weeks was lower: 0.90 (95% CI, 0.85-0.94) and 0.85 (95% CI, 0.80-0.90), respectively. The optimal single sFlt-1/PlGF ratio threshold for all preeclampsia and late-onset preeclampsia within 1 and 4 weeks was 66. The negative and positive predictive values for ruling out and ruling in developing preeclampsia within 1 week were 96% and 70%, respectively. Conclusions The Kryptor sFlt-1/PlGF ratio is a useful clinical tool ruling out and in preeclampsia within 1 week. Prediction within 4 weeks is superior for early-onset preeclampsia. A single decision threshold of 66 is indicated for use in clinical routine.

Enhancing the value of the sFlt-1/PlGF ratio for the prediction of preeclampsia: Cost analysis from the Belgian healthcare payers' perspective

OBJECTIVE

To evaluate the economic impact of introducing the soluble fms-like tyrosine kinase (sFlt-1) to placental growth factor (PlGF) ratio test into clinical practice in Belgium for the prediction of preeclampsia (PE).

STUDY DESIGN

We developed a one-year time-horizon decision tree model to evaluate the short-term costs associated with the introduction of the sFlt-1/PlGF test for guiding the management of women with suspected PE from the Belgian public healthcare payers' perspective. The model estimated the costs associated with the diagnosis and management of PE in pregnant women managed in either a test scenario, in which the sFlt-1/PlGF test is used in addition to current clinical practice, or a no test scenario, in which clinical decisions are based on current practice alone. Test characteristics were derived from PROGNOSIS, a non-interventional study in women presenting with clinical suspicion of PE. Unit costs were obtained from Belgian-specific sources. The main model outcome was the total cost per patient.

RESULTS

Introduction of the sFlt-1/PlGF ratio test is expected to result in a cost saving of €712 per patient compared with the no test scenario. These savings are generated mainly due to a reduction in unnecessary hospitalizations.

CONCLUSIONS

The sFlt-1/PlGF test is projected to result in substantial cost savings for the Belgian public healthcare payers through reduction of unnecessary hospitalization of women with clinical suspicion of PE that ultimately do not develop the condition. The test also has the potential to ensure that women at high risk of developing PE are identified and appropriately managed.

Unravelling the potential of angiogenic factors for the early prediction of preeclampsia

Preeclampsia is a multisystem, multiorgan hypertensive disorder of pregnancy responsible for maternal and perinatal morbidity and mortality in low- and middle-income countries. The classic diagnostic features hold less specificity for preeclampsia and its associated adverse outcomes, suggesting a need for specific and reliable biomarkers for the early prediction of preeclampsia. The imbalance of pro- and antiangiogenic circulatory factors contributes to the pathophysiology of preeclampsia. Several studies have examined the profile of angiogenic factors in preeclampsia to search for a biomarker that will improve the diagnostic ability of preeclampsia and associated adverse outcomes. This may help in more efficient patient management and the reduction of associated health care costs. This article reviews the findings from previous studies published to date on angiogenic factors and suggests a need to apply a multivariable model from the beginning of pregnancy and continuing throughout gestation for the early and specific prediction of preeclampsia.

Gestational Age-Specific Reference Ranges for the sFlt-1/PlGF Immunoassay Ratio in Twin Pregnancies

OBJECTIVE

Establish reference ranges for the Elecsys® soluble fms-like tyrosine kinase-1 (sFlt-1)/placental growth factor (PlGF) immunoassay ratio in twin pregnancies.

METHODS

Data analyzed were from 3 prospective studies: Prediction of Short-Term Outcome in Pregnant Women with Suspected Preeclampsia (PE) (PROGNOSIS), Study of Early-onset PE in Spain (STEPS), and a multicenter case-control study. Median, 5th, and 95th percentiles for sFlt-1, PlGF, and the sFlt-1/PlGF ratios were determined for normal twin pregnancies for 7 gestational windows and compared with the previous data for singleton pregnancies.

RESULTS

The reference range analysis included 269 women with normal twin pregnancies. Before 29 weeks' gestation, median, 5th, and 95th percentiles for sFlt-1/PlGF ratios did not differ between twin and singleton pregnancies. From 29 weeks' gestation to delivery, median, 5th, and 95th percentiles for sFlt-1/PlGF ratios were substantially higher in twin versus singleton pregnancies. sFlt-1 values were higher in women with twin pregnancies across all gestational windows. PlGF values were similar or higher in twin versus singleton pregnancies; PlGF concentrations increased from 10 weeks + 0 days to 28 weeks + 6 days' gestation.

CONCLUSIONS

Reference ranges for the sFlt-1/PlGF ratio are similar in women with twin and singleton pregnancies until 29 weeks' gestation but appear higher in twin pregnancies thereafter.

Short-term prediction of preeclampsia using the sFlt-1/PlGF ratio: a subanalysis of pregnant Japanese women from the PROGNOSIS Asia study

Two prospective multicenter studies demonstrated that a soluble fms-like tyrosine kinase 1 (sFlt-1)/placental growth factor (PlGF) ratio cutoff of ≤38 can rule out preeclampsia within 1 week with a negative predictive value (NPV) of 99.3% (PROGNOSIS) and 98.6% (PROGNOSIS Asia). We report a subanalysis of the Japanese cohort from the PROGNOSIS Asia study. Pregnant women with suspected preeclampsia between gestational weeks 18 + 0 days and 36 + 6 days were enrolled at eight Japanese sites. Primary objectives: Assess the performance of the Elecsys^® sFlt-1/PlGF ratio cutoff ≤38 to rule out preeclampsia within 1 week and of the cutoff >38 to rule in preeclampsia within 4 weeks. Key secondary objectives: Prediction of maternal and fetal adverse outcomes (MAOs/FAOs) and their relationship with duration of pregnancy. Of 192 women enrolled, 180 (93.8%)/175 (91.1%) were evaluable for primary/combined endpoint analyses. Overall preeclampsia prevalence was 13.3%. A sFlt-1/PlGF ratio of ≤38 provided an NPV of 100% (95% confidence interval [CI], 97.5–100) for ruling out preeclampsia within 1 week, and a ratio of >38 provided a positive predictive value of 32.4% (95% CI, 18.0–49.8) for ruling in preeclampsia within 4 weeks. The area under the curve for the prediction of preeclampsia/maternal/fetal adverse outcomes within 1 week was 94.2% (95% CI, 89.3–97.8). After adjusting for gestational age and final preeclampsia status, Cox regression indicated a 2.8-fold greater risk of imminent delivery for women with a sFlt-1/PlGF ratio >38 versus ≤38. This subanalysis of Japanese women with suspicion of preeclampsia showed high predictive value for a Elecsys sFlt-1/PlGF ratio cutoff of 38 for short-term prediction of preeclampsia.

Applying the concept of uncertainty to the sFlt-1/PlGF cut-offs for diagnosis and prognosis of preeclampsia

OBJECTIVES

Placental growth factor (PlGF) and soluble fms-like tyrosine kinase-1 (sFlt-1) assays and the corresponding ratios (sFlt-1/PlGF) have been proposed to aid in the diagnosis by exclusion and/or prognosis of preeclampsia (PE). A method for evaluating ratio uncertainties (RUs), based on the theory of error propagation, was applied to the sFlt-1/PlGF ratio.

METHODS

RUs were calculated using data derived from sFlt-1 and PlGF Internal Quality Control (IQC) results collected from four centers using Elecsys (Roche) or Kryptor (Thermo Fisher) sFlt-1 and PlGF assays. The corresponding ratio uncertainties were defined for each ratio value.

RESULTS

The RUs increased linearly with the sFlt-1/PlGF ratio values. The Elecsys RUs were lower than the Kryptor RUs. Although RUs cannot eliminate differences in ratio values observed among various immunoassays, it can affect interpretation of the sFlt-1/PlGF ratio, especially when results are within the range of predefined PE diagnosis or prognosis cut-offs.

CONCLUSIONS

Since RUs are only a function of PlGF and sFlt-1 precision, they can be calculated for each assay from each laboratory to adjust the interpretation of sFlt-1/PlGF ratio results in the context of PE.

Single-Tube Multimarker Assay for Estimating the Risk to Develop Preeclampsia

BACKGROUND

Preeclampsia (PE) affects 2%-8% of all pregnancies worldwide. The predictive value of the currently used maternal serum fms-like tyrosine kinase-1/ placental growth factor (sFlt-1/PlGF) test is < 40% for PE onset within 4 weeks. We aimed to develop an innovative multiplex assay to improve PE prediction.

METHODS

The 6PLEX assay combining the measurements of ADAM12, sENG, leptin, PlGF, sFlt-1, and PTX3 was developed for the Luminex® xMAP platform. Assay performance was evaluated using 61 serum samples drawn from 53 pregnant women between 180 and 275 gestational days: diagnosed PE cases, n = 4; cases with PE onset within 4-62 days after sampling, n = 25; controls, n = 32. The B·R·A·H·M·S Kryptor sFlt-1/PlGF test (Thermo Fisher Scientific, Hennigsdorf, Germany) was applied as an external reference. Alternative PE prediction formulae combining 6PLEX measurements with clinical parameters were developed.

RESULTS

There was a high correlation in sFlt-1/PlGF estimated for individual sera between the 6PLEX and B·R·A·H·M·S Kryptor immunoassays (Spearman's r = 0.93, P < 0.0001). The predictive power of the 6PLEX combined with gestational age and maternal weight at sampling reached AUC 0.99 (95% CI 0.97-1.00) with sensitivity 100.0% and specificity 96.9%. In all models, sFlt-1/PlGF derived from the B·R·A·H·M·S immunoassays exhibited the lowest AUC value (<0.87) and sensitivity (<80%) with broad confidence intervals (13%-92%). The estimated prognostic yield of the 6PLEX compared to the B·R·A·H·M·S assay was significantly higher (96.5% vs 73.7%; P = 0.0005).

CONCLUSIONS

The developed single-tube multimarker assay for PE risk estimation in combination with clinical symptoms reached high prognostic yield (96.5%) and exhibited superior performance compared to the sFlt-1/PlGF test.

Correlation of Kryptor and Elecsys® immunoassay sFlt-1/PlGF ratio on early diagnosis of preeclampsia and fetal growth restriction: A case-control study

OBJECTIVES

The measurement of the soluble fms-like tyrosine kinase-1 to placental growth factor (sFlt-1/PlGF) ratio on automated platforms has improved the detection of preeclampsia and fetal growth restriction (PE/FGR). The cut-off points of >38 and ≥85 has been defined for "rule in" and "aid in diagnosis", respectively, using the Elecsys® platform. We aimed to compare the performance of these cut-offs between the Elecsys® and Kryptor platforms at 24-28 weeks.

STUDY DESIGN

Observational case-control study of singleton pregnancies at high risk for PE/FGR and sFlt-1/PlGF measurement at 24-28 weeks' gestation: 21 cases (9 early PE/FGR with delivery <32 weeks) were 1:1 matched for body mass index and parity with 21 controls. Correlations of the sFlt-1, PlGF and sFlt-1/PlGF values and diagnostic accuracy of the >38 and ≥85 cutoffs for early and late PE/FGR using Elecsys® and Kryptor assays were evaluated.

MAIN OUTCOME MEASURES

PE/FGR cases showed significantly higher median (IQR) sFlt-1/PlGF values at 24-28 weeks vs. controls, using both Elecsys® and Kryptor platforms: 55 (13-254) and 97 (13-530) vs. 4.1 (2.0-6.5) and 3.9 (1.8-7.7), respectively. The sFlt-1/PlGF correlation between both methods was excellent (r² = 0.95) although lower PlGF and higher sFlt-1/PlGF values were observed with Kryptor. The higher diagnostic accuracy was obtained for early PE/FGR with the ≥85 cutoff (95.2%; 95%CI: 83.8-99.4%) in both platforms.

CONCLUSION

sFlt-1/PlGF measurements correlates well between Elecsys® and Kryptor platforms, and the cutoffs of >38 and ≥85 exhibit high diagnostic accuracy for assessing early PE/FGR at 24-28 weeks with both methods.