#NephJC Chat
Tuesday, March 26th, 2024, 9 pm Eastern (AEST = March 26th, 11 am)
Wednesday, March 27th, 2024, 9 pm Indian Standard Time and 3:30 pm GMT (AEST = March 27th, 2 am)
NEJM Evid. 2022 Dec;1(12):EVIDoa2200161.
doi: 10.1056/EVIDoa2200161. Epub 2022 Nov 9
Circulating Angiogenic Factor Levels in Hypertensive Disorders of Pregnancy
Ravi Thadhani, Elizabeth Lemoine, Sarosh Rana, Maged M. Costantine, Vinicius F. Calsavara, Kim Boggess, Blair J. Wylie, Tiffany A. Moore Simas, Judette M. Louis, Jimmy Espinoza, Stephanie L. Gaw, Amy Murtha, Samantha Wiegand, Yvonne Gollin, Deepjot Singh, Robert M. Silver, Danielle E. Durie, Britta Panda, Errol R. Norwitz, Irina Burd, Beth Plunkett, Rachel Scott, Anna Gaden, Martha Bautista, Yuchiao Chang, Marcio A. Diniz, S. Ananth Karumanchi, and Sarah Kilpatrick
PMID: 38319832
Introduction
As March unfolds, NephMadness anticipation builds; therefore, this summary aims to align with the preeclampsia region. Before we start, as nephrologists, we’ll take this rare opportunity and remember that, despite common beliefs, glomerular injury of preeclampsia (PE) is the most common glomerular disease in the world (and not IgAN!). PE is a complex multisystemic hypertensive disorder complicating about 5% of pregnancies with a wide variation across the regions and is a major cause of maternal and fetal mortality and morbidity (Abalos et al, Eur J Obstet Gynecol Reprod Biol, 2013). The rates of hypertensive disorders during pregnancy have been on the rise due to an increase in the prevalence of chronic hypertension and obesity. In addition, specific populations, like Black and Hispanic women, have up to twice the risk of preeclampsia as their White counterparts (Gyamfi-Bannerman C et al, Matern Fetal Neonatal Med 2020). In preeclampsia, abnormal placentation and maternal vascular dysfunction lead to reduced blood flow, causing an imbalance in angiogenic factors. Specifically, levels of the antiangiogenic factor soluble fms-like tyrosine kinase 1 (sFlt-1) rise while levels of its ligand, placental growth factor (PlGF), decline. This imbalance precedes clinical symptoms and correlates with disease severity (Rana et al, Circulation 2012, Salahuddin et al, Hypertens Pregnancy, 2016).
Figure 1. Pathophysiology of Preeclampsia, from Divya Bajpai et al. Kidney 360, 2023
For now, as recommended by the American College of Obstetrics and Gynecology (ACOG), preeclampsia is diagnosed starting with hypertension, accounting for multiple organs and systems involved (as detailed in table S2 from Thadhani et al, NEJM Evid 2022). Meeting the diagnostic criteria is laborious and it doesn’t differentiate severe forms of preeclampsia (sPE). Using the pathophysiological understanding of PE, the ratio between anti-angiogenic and angiogenic factors has been proposed as a diagnostic and prognostic biomarker (sFlt-1:PIGF ratio).
Summing up, the sFlt-1:PIGF ratio already been validated in Europe based on prospective validation cohort studies like PROGNOSIS (Hund et al, BMC Preg Child 2014), and SaPPPhire meta-analysis (Agrawal et al, Hypertension 2018). In the PROGNOSIS study, the ratio had a high negative predictive value to predict the absence of preeclampsia with an sFlt-1:PIGF ratio of 38 or lower. However, the existing studies have several limitations, including the heterogeneity of the populations and the cut-off points. (see table below)
The sFLT-1:PlGF ratio had not been validated in large-scale studies in the US and was, therefore, not included in the ACOG’s national practice guidelines for preeclampsia diagnosis.
In the PRAECIS trial (Preeclampsia Risk Assessment: Evaluation of Cut-offs to Improve Stratification), the investigators sought to determine if assessing serum biomarkers (a cornerstone of PE development) could help predict and stratify risk for developing sPE, as well as adverse outcomes.
The Study
Methods
PRAECIS is a multicenter, blinded prospective study consisting of 2 cohorts, where the ratio of sFlt-1:PlGF was measured in pregnant women hospitalized with a hypertensive disorder. A derivation cohort was initially used to determine the cutoff values for the sFlt-1/PlGF to discriminate between women who were more likely to develop severe preeclampsia (sPE) from those who would not. These cutoff values were then tested in another validation cohort.
Study population
Hospitalized women were included from 18 US hospitals with the features described in the table. Notably, women with sPE were excluded.
Preeclampsia and other hypertensive disorders of pregnancy were defined according to ACOG 2013 (table S2). Noteworthy, since 2013, proteinuria has not been a mandatory feature to diagnose PE.
Table S2. Study Population. Thandhani et al. NEJM Evid 2022
Study plan
After informed consent, a blood sample for assessing sFlt-1/PlGF was drawn from each participant. Their outcomes were followed for two weeks or until delivery, whichever occurred first. Women who did not deliver within 2 weeks could be re-consented and re-enrolled, thereby resetting the 2-week clock with an updated enrollment blood sample. All investigators, patients, and clinicians were blinded to the sFlt-1/PlGF measurements. It was batch-analyzed after recruitment of the last participant in each cohort, so the results didn’t alter the clinical management during the study.
Primary Endpoints
For both derivation and validation cohorts, the primary endpoint was defined by sPE within two weeks from testing.
An adjudication committee of maternal-fetal medicine experts blinded to the local diagnosis was to assess whether a participant met the criteria for sPE at enrollment or within 2 weeks. Outcome confirmation was agreed to by two committee members, and a third member served as a tiebreaker in cases of disagreement.
Secondary endpoints
There were three categories of composite secondary outcomes: maternal adverse events, fetal/ neonatal adverse events, and performance of sFLT1/PIGF ratio, as depicted in the table.
Statistical Analysis
The sample size calculation was based on the primary objective, which was to derive a sFlt-1:PlGF ratio cut-off value to predict the development of sPE within two weeks of measurement. In the derivation cohort, the investigators identified the cutoff of the sFlt-1:PlGF ratio that provided the highest sensitivity and a minimum specificity of 70%. The calculated sample size was 215 unique participants based on sPE prevalence of 33.5% in hospitalized women with a hypertensive disorder of pregnancy (Rana, et al. Pregnancy Hypertens 2018). Considering a dropout rate of 15%, a minimum sample size of 250 unique patients would be included in part 1 of the study. For the validation cohort, the sample size calculations suggested at least 477 unique participants would provide 86% power for sensitivity and 99% power for specificity yielding a joint power of at least 86% for the ratio cut-off identified in the derivation cohort.
In the validation cohort, the hypothesis that sensitivity and specificity were at least 70% in the validation cohort was tested with 95% confidence intervals (CIs). The discrimination ability of biomarkers was quantified by using the area under the receiver-operating characteristic curve (AUC) with 95% CIs, comparing the sFlt-1:PlGF ratio versus routinely measured parameters: systolic and diastolic blood pressures, liver and kidney function tests, and platelet counts. Multivariable proportional hazards Cox models were fitted as a function of the binary sFlt-1:PlGF ratio and known risk factors and confounders of preeclampsia (maternal age, parity, enrollment gestational age, highest systolic blood pressure at enrollment, and laboratory tests at enrollment as continuous variables.
Results
The study ran from 2019 to 2021, involving 1014 women from 18 US hospitals. Common comorbidities included chronic hypertension in half of the participants, preeclampsia in a quarter, and diabetes mellitus in 13%. Ten percent were current smokers. Less than 5% had a history of kidney disease, and SLE. Among the included population, 299 were in the derivation cohort and 715 in the validation cohort. (Figure S1)
Figure S1. Consort diagram for derivation and validation cohort from Thadani R, et al, NEJM Evid 2022
Derivation Cohort
In 13 hospitals with an initial enrollment of 299 women, only 220 were finally included because the rest 79 had sPE during presentation. Of the 220 patients included, the mean age of patients was 31.9 years. Although the predominant was White/Caucasian (47.7%), one-third of the patients were Black, and almost 10% were Hispanic.
One-third of patients were nulliparous, and less than half of women in both groups had used ASA. The group without sPE had slightly increased blood pressure and proteinuria, too, with no differences in creatinine levels between groups during the study period and delivery. For the gestational age at delivery, women with sPE had an earlier delivery, and babies had < 2000 grams of weight.
Women who developed sPE within two weeks had a higher median sFlt-1:PIGF ratio (200; IQR, 53 to 458) than those who did not (6; IQR, 3 to 26; p<0.001). The incidence within two weeks of sPE was 31%. Among the women with sPE, SBP and DBP were higher.
Table 1. Demographic and Clinical Characteristics of the Primary Study Population (Derivation Cohort), from Thadani R, et al, NEJM Evid 2022
An sFlt-1:PlGF ratio >40 showed 81% sensitivity (95% CI, 70 to 90) and 81% specificity (95% CI, 74 to 87) with a PPV of 66% (95% CI, 55-76) and an NPV of 90% (95% CI, 84-95) for the primary outcome. This sFlt-1:PlGF ratio >40 obtained from the derivation cohort was further tested in the validation cohort (see figure S3 below).
Validation Cohort
The validation cohort included 556 women who were enrolled. They were expected to resemble those in the derivation cohort and had no sPE at admission. The incidence of sPE in this group within 2 weeks was 33.5%.
The median sFlt-1:PlGF ratios were approximately 40 times higher in women who developed sPE than those who did not (291 [IR, 121–777] vs 7 [IR, 3–40]). When the analysis was restricted to only one (first or last) enrollment per patient, it still gave similar results. (Figure 1)
Figure 1a. Serum sFlt-1:PIGF Ratio in Women Who Develop or Do Not Develop sPE over 2 Weeks, from Thadani R, et al, NEJM Evid 2022.
The sFlt-1:PlGF ratio >40 showed 94% sensitivity (95% CI, 89-96) and 75% specificity (95% CI, 70-79) with a PPV of 65% (95% CI, 59-71) and a NPV of 96% (95% CI, 93-98) for the primary outcome. The PPV and NPV were similar in black and women with hypertension. Race-specific multiples of the median of the sFlt-1:PlGF ratio were also higher for Black women compared with White or Asian women.
Figure 2. Predictive Accuracy for Serum sFlt-1: PIGF Ratio and Other Standard-of-Care Test for the Development of sPE, from Thadani R, et al, NEJM Evid 2022.
When comparing the predictive accuracy of the serum sFlt-1:PIGF ratio to the other standard-of-care, the AUC for the ratio was 0.92 (95% CI, 0.89-0.94), whereas all other routine measures had an AUC <0.75 (including clinician’s trustful hypertension). Adjustments for gestational age, blood pressure, or blood tests did not improve its accuracy.
Adverse outcomes associated with high sFlt-1:PIGF ratios at enrollment
In the validation cohort comprising 556 patients, 51 experienced adverse maternal outcomes. Those who had adverse outcomes exhibited a significantly higher sFLT-1:PlGF ratio compared to those who didn't (279 [IC, 53 to 774] vs. 22 [IR, 4 to 171], respectively).
Composite adverse maternal outcomes were more prevalent in patients with a ratio ≥40 compared to those with a ratio <40. The relative risk for severe thrombocytopenia and elevated liver enzyme levels was notably high (risk ratios of 9.7 and 14.1, respectively) in this group.
Among the 556 pregnant women, 288 had adverse fetal and neonatal outcomes. The sFlt-1:PlGF ratio was higher in women with adverse fetal and neonatal outcomes compared to those without (182 vs. 6).
Figure 3. Adverse Outcomes and Time to Delivery in the Primary Study Population. Panel A: Distributions of sFlt-1:PIGF ratios (vertical axis log-scaled) in strata according to composite maternal adverse outcomes (left panel) and composite fetal outcomes (right panel) from Thadani R, et al, NEJM Evid 2022.
Composite adverse fetal and neonatal outcomes were more prevalent in the group with an sFlt-1:PIGF ratio ≥40 compared with the group with a ratio <40. Notably, eight of nine fetal deaths were in the group with a ratio ≥40; this group had a 22% higher incidence of low weight for gestational age compared to a ratio <40.
Table 3. Adverse Outcomes Associated with sFlt-1:PIGF Ratios, from Thandhani et al. NEJM
Women with an sFlt-PLGF ratio ≥40 were more likely to deliver within two weeks than women with a ratio <40. (74.4% vs 32.6%). The hazard ratio for delivery remained >3 after adjustment for maternal age, parity, gestational age at presentation, and highest systolic blood pressure.
Figure 3b. Kaplan Meier plot for the probability of remaining undelivered (vertical- %) in strata according to binary sFlt-1:PIGF ratio cutoff 40 for all enrollments is depicted, from Thadani R et al, NEJM Evid 2022.
Interestingly, with higher sFLT1:PIGF ratios, percentage of remaining undelivered within next two weeks is lower, even in the reference quartile with sFLT1:PIGF ratio <40 (HR 1.3). Therefore, in quartiles 3 (ratio 34.1-221) and 4 (ratio 221-7270), there is a 3-6 times lower chance of staying undelivered.
Figure 3c. Kaplan-Meier plot for the probability of remaining undelivered in strata according to quartiles of the sFlt-1:PIGF ratio, from Thadani R, et al, NEJM Evid 2022.
False negative and false positive findings
There were 12 women with an sFlt-1:PIGF ratio <40 but who developed sPE within two weeks. The majority were among women with chronic hypertension.
Ninety-three women with an sFlt-1:PIGF ratio ≥40 did not subsequently develop sPE (false positive test results).
Fifty-three of 93 patients had adverse fetal or neonatal outcomes. Of these 93 women without sPE, those with a ratio ≥40 delivered earlier (median, 19 days) compared with those with a ratio <40 (median, 29 days).
Discussion
In this study, serum sFLT-1:PIGF ≥40 indicates a higher risk of developing sPE within the next two weeks in women hospitalized with hypertensive disorders of pregnancy than in women with ratios <40, with a positive predictive value of 65%. Additionally, the ratio was linked to a higher risk of adverse outcomes associated with pregnancy and time to delivery.
The women with an sFlt-1:PIGF ratio <40 had a <5% chance of developing sPE within 2 weeks.
In the PRAECIS study, the comorbidities observed were predominantly chronic hypertension in half of the population. Chronic hypertension increases the risk of maternal adverse outcomes including preeclampsia. An analysis (Ananth CV et al, Hypertension 2019) including over 151 million pregnancies in the U.S. revealed a concerning trend in chronic hypertension among pregnant women in the U.S. Over four decades, the overall prevalence has risen, with black women experiencing more than double the rate compared to white women. This fact further underlines the importance and need for a more diverse and representative cohort for the US, while the PROGNOSIS study (Zeisler et al, NEJM 2016), the European validation cohort, has a more homogenous population. The PROGNOSIS study did reveal that an sFlt-1:PIGF ratio of 38 had a positive predictive value of 36.7% within 4 weeks for predicting preeclampsia or hemolysis, elevated liver enzymes, and low platelet count syndrome. We would not call it an improvement in test performance, but rather will underline that the reason is a better outcome predicting tool for a shorter term (2 weeks in the US cohort, compared with 4 weeks in Europe’s validation cohort). Furthermore, the women in PRAECIS had more severe disease requiring hospitalization. The number of maternal adverse outcomes reported was 10%, in contrast with prior studies <1.
“Children of women with renal disease used to be born dangerously or not at all”
More in the nephrology realm, pregnancy in CKD is not a rare occurrence, as a Lancet editorial stated in 1975. CKD is estimated to affect 3% of pregnant women in high-income countries (Piccoli GB et al, CJASN, 2010), so as nephrologists, we will face more often the almost impossible-to-respond question: chronic hypertension vs superimposed preeclampsia? sFlt-1:PIGF ratio would also be helpful in this kind of situation. One prospective cohort study revealed that PIGF <12 pg/mL has an accuracy comparable to that of patients without CKD (sensitivity 60%, specificity 78.9%, PPV 54.5%, NPV 94.6%). (Bramham K et al, Kidney Int, 2016)
Limitations
The study did not include women with multiple fetus pregnancies, and women with gestational age between 20 and 22 weeks, and the validity of these biomarker ratios in such women is unclear. Similarly, the patients receiving heparin were excluded and these women may have underlying diseases like APLA which is known to cause PE by causing thrombosis of placental vessels. Also, the study did not address outpatient women with PE and whether it could have altered the results in any way is not known.
Conclusion
The multicenter cohort of pregnant women with hypertension hospitalized between 23 and 35 weeks of gestation, a serum sFlt-1:PIGF ratio of 40 predicted the development of sPE, adverse outcomes, and delivery within two weeks of testing. Notably, this was a landmark trial, and it led to FDA clearance of these biomarkers for risk assessment and clinical management of pregnant women with preeclampsia.
Summary by
Elba Medina,
Assistant Professor,
Hospital General de México "Dr. Eduardo Liceaga"
Mexico City, Mexico
and
Kavita Vishwakarma,
Consultant Nephrologist,
Bhaktivedanta Hospital & Research Institute
Maharashtra, India
NephEdC (NSMC) Interns, Class of 2024
Reviewed by Cristina Popa, Husam Alzayer, Pallavi Prasad