Preterm birth (PTB) is one of the leading causes of neonatal mortality and morbidity worldwide. Early identification of women and patients at risk of spontaneous preterm birth (sPTB) allows for timely interventions, such as corticosteroids, which can improve outcomes. The accuracy of point-of-care (POC) diagnostic tests is critical in reducing unnecessary hospital admissions and ensuring optimal resource allocation in the NHS. Recent evidence from a comprehensive meta-analysis provides valuable insights into the comparative performance of three biomarker tests:
1) PartoSure - utilising the placental alpha-microglobulin-1 (PAMG-1) biomarker
2) Actim Partus - utilising the phosphorylated insulin-like growth factor-binding protein-1 (phIGFBP-1) biomarker
3) and fetal fibronectin (fFN)
Since the discontinuation of fetal fibronectin as a preterm labour test was announced in 2024, it is critical to assess the viability and efficacy of the remaining tests available.
Comparing PAMG-1, fFN, and phIGFBP-1: A Meta-Analysis Overview
A systematic review and meta-analysis of multiple cohort studies assessed the diagnostic accuracy of these biomarkers in predicting PTB within 7 days of testing in symptomatic women. The key findings include:
Sensitivity (ability to correctly identify true cases of PTB ≤7 days):
PAMG-1: 76%
fFN: 58%
phIGFBP-1: 93%
Specificity (ability to correctly exclude false positives):
PAMG-1: 97%
fFN: 84%
phIGFBP-1: 76%
Positive Predictive Value (PPV, likelihood that a positive result correctly predicts PTB ≤7 days):
PAMG-1: 76.3%
fFN: 34.1%
phIGFBP-1: 35.2%
Negative Predictive Value (NPV, likelihood that a negative result correctly rules out PTB ≤7 days):
PAMG-1: 96.6%
fFN: 93.3%
phIGFBP-1: 98.7%
Why PAMG-1 is the Most Accurate Test
The meta-analysis confirmed that PAMG-1 (PartoSure) had the highest combination of PPV and specificity, making it the most reliable test for predicting imminent preterm birth. Unlike phIGFBP-1, which has a high false-positive rate leading to unnecessary admissions and interventions, PAMG-1 offers a more targeted and effective approach. While phIGFBP-1 had the highest sensitivity, its lower specificity reduces its clinical utility for decision-making.
Clinical Implications for UK Obstetric Practice
The findings suggest that PAMG-1 testing should be utilised in NHS maternity units for assessing women presenting with symptoms of preterm labour. Implementing PAMG-1 as the primary biomarker test can:
Reduce unnecessary admissions and interventions: Fewer false positives mean fewer hospitalisations and resource usage.
Improve risk stratification: More accurate identification of high-risk women ensures timely administration of interventions and in-utero transfers if needed.
Enhance patient experience: PAMG-1 requires a simple, non-invasive vaginal swab without the need for a speculum examination, improving patient comfort.
Conclusion
The results of the meta-analysis suggest that incorporating PAMG-1 testing into routine clinical practice for preterm birth risk assessment offers an improvement in diagnostic accuracy compared to phIGFBP-1. Utilising PAMG-1 for PTB prediction in symptomatic patients represents the favourable option for reducing unnecessary interventions while ensuring women and patients at risk receive the necessary timely care.
Find a full literature summary comparing preterm labour test accuracy here.
Reference:
Melchor JC, Khalil A, Wing D, Schleussner E, Surbek D. Prediction of preterm delivery in symptomatic women using PAMG-1, fetal fibronectin and phIGFBP-1 tests: systematic review and meta-analysis. Ultrasound Obstet Gynecol. 2018 Oct;52(4):442-451. doi: 10.1002/uog.19119. Epub 2018 Sep 4. PMID: 29920825.
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