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• W2800502425 abstract "There has been considerable effort in recent years to untangle the enigma of spontaneous preterm birth – and rightly so, given its extraordinary clinical, personal and economic impact. This issue of the Journal illustrates the range of predictive tests and interventions under investigation. The plethora of reports can be confusing, often with conflicting evidence and highly dependent on the populations investigated, and sometimes with competing commercial and academic interests. Yet, this increasing evidence base is welcomed, if we are to make headway with resolving the various controversies. A number of tests predictive for preterm labor are currently being marketed. Just as the efficacy and clinical utility of interventions are dependent on the population in which they are used, the same is true for prediction tests. The purpose of prediction may vary, for example to determine delivery risk in the short term for women with threatened preterm birth or in the long term for asymptomatic high-risk women. In symptomatic women, determining immediate management options, such as administration of antenatal corticosteroids for fetal lung maturation, or selection of place of birth to ensure optimal neonatal care, is valuable. For asymptomatic women, antenatal management plans, including risk modification (by, for example, stopping smoking) and targeting of prophylactic interventions (such as cervical cerclage, pessary or progesterone), are relevant. For both groups, there is considerable value in the reassurance provided by negative or low-risk results. Cervical-length measurement and fetal fibronectin testing (Hologic) can be used in both asymptomatic and symptomatic women, while the Actim Partus (Medixbiochemica) and PartoSure (Parsagen Diagnostics, Inc.) tests are reliable only in symptomatic women. With increasing evidence in support of various interventions in asymptomatic women, it may be inappropriate to adopt one test to the exclusion of another because of evidence based on one particular clinical use. In the future, predictive tests may not be mutually exclusive; for example, the best test for symptomatic prediction may be different from that for asymptomatic prediction; but they may possibly be used in combination (such as cervical length with a biomarker). Traditionally, preterm prediction tests have been marketed to have high rule-out capabilities in symptomatic women, in order to avoid unnecessary intervention. This strategy has clinical utility given the low prevalence of preterm birth within 7 days from testing (often <5%). Avoiding both unwarranted antenatal bed occupancy (including blocking neonatal cots) and babies receiving unnecessary or poorly timed antenatal steroids is highly desirable. Recent evidence suggests that timing is more critical than previously thought, and the best outcomes occur if steroids are administered to the mother within 48 h prior to delivery1. Clinicians are often reluctant to give a second course for fear of fetal growth restriction; this results in most preterm neonates <35 weeks' gestation not receiving antenatal steroids within 7 days of delivery (beyond which there is little evidence of benefit). This is because most women who receive steroids do not deliver within a week. Withholding steroids in women initially, unless risks are very high, is likely to increase the chance that the baby will receive a dose closer to birth, which in turn will reduce adverse outcomes such as mortality and neonatal intracerebral hemorrhage. A good rule-out test gives clinicians the confidence to do this. Overall, this strategy may result in more babies receiving optimal treatment. As delivery within a week is rare, even a poor test may have a high negative predictive value (NPV) and this statistic is often used in marketing literature to make a product look impressive, even though the added value of the test is minimal. A paper in this issue2 illustrates this low prevalence, finding that fewer than 5% of women delivered in a week, meaning the ‘worst’ NPV the test could have was 95%, which, in fact, can be achieved even if the test is no better than chance. In this study, both the PartoSure test and fetal fibronectin level had poor sensitivity of 50% or lower, which means that at least half of women delivering early would be reassured falsely by the test. This is worrying, as it is dangerous to send women home or withhold steroids when delivery is imminent. Concerns over false-negative tests have resulted in the National Institute of Health and Care Excellence in the UK recommending not to use predictive tests < 30 weeks' gestation3 and we have to find better prediction strategies. Clinicians should scrutinize false-negative rates and sensitivity before relying on a test, as the NPV is driven principally by the event rate, which, in turn, is dependent on the study population. In the Melchor study2, the old qualitative fetal fibronectin test was used at a threshold of 50 ng/mL, and this has now been largely superseded by a quantitative test that allows clinicians to use different thresholds according to need. A lower threshold of 10 ng/mL has much higher sensitivity. By combining these biomarkers with cervical length, adequate rule-out performance with minimal false-negative tests can be achieved4. An economic evaluation in this issue demonstrates cost savings when cervical length between 15 and 30 mm is combined with fetal fibronectin in symptomatic women to inform management of threatened preterm labor5. The future of predicting preterm birth will need to be more discerning, and research will need to consider combining clinical with biophysical/biochemical tests. Interventions in asymptomatic women also have varying efficacy according to the population in which they are studied. A number of conflicting studies have been published in recent years evaluating the benefit of the vaginal pessary to prevent preterm birth. This flexible silicone ring, which is inserted in early pregnancy, can also be removed easily near term, making it an attractive alternative to cerclage. It can be associated with profuse vaginal discharge, which may cause confusion over whether membranes have ruptured, but otherwise appears to be innocuous. Studies in both twins and singletons have been conflicting. In this issue, a long-term follow-up study of one of the successful twin trials is presented; it is reassuring that improved survival was not associated with worse neurodevelopmental outcome6. This study defined a short cervix, unconventionally, as 38 mm, again demonstrating the heterogeneity of the studied populations. We await further studies in twins to add to the growing evidence and to clarify the variable results from other studies and possible explanations to account for these. Another study in this issue considers the value of pessary placement in low-risk singleton pregnancy (without prior preterm birth). In 122 women with cervical length < 20 mm, those who received a pessary were no more likely to deliver preterm than were those who did not (43% vs 40%; relative risk, 1.09 (95% CI, 0.71–1.68))7. This study confirms that women with a short cervix are at high risk of early delivery but is at variance with other recent low-risk studies suggesting substantial benefit of pessary use8. There are international groups planning an individual patient data analysis to help resolve this controversy. Perhaps one of the key questions is how does pessary compare with cerclage and progesterone, and should they be used in combination? Twin pregnancy and etiological factors/risk status may also influence efficacy. It will take considerably more evidence to refine the indications for these interventions. A key question is whether all pregnant women should be screened routinely and those with a short cervix (usually < 25 mm) treated. This practice has been advocated for progesterone, although the cost implications and efficacy probably do not justify this. A further paper in this issue illustrates the problem of screening low-risk women for short cervical length9; although a short cervix < 25 mm is a major risk factor for early delivery, when the numbers needed to treat and treatment efficacy were considered, it was estimated that 1500 women would have to be screened to prevent one preterm birth. Cervical length may be less valuable in different populations; another paper in this issue demonstrates poor prediction in asymptomatic triplets10, although when cervical length is combined with biochemical markers in triplets, this may be improved11. The subtleties of differing efficacy in both prediction and prevention of preterm birth, related to populations and agents used, will continue to evolve. Combining tests, particularly cervical length with biochemical markers, could improve clinical utility. Prevention is the ideal aim, and markers that can direct prophylactic therapies are needed. The evidence base for these interventions will require considerably more effort from our academic community. In the meantime, clinicians must be willing to contribute to clinical trials and act on the findings of secondary analysis, collating evidence whenever possible, and not be swayed by enthusiasm engendered from the latest trial." @default.
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• W2800502425 title "Prediction and prevention of preterm birth: a quagmire of evidence" @default.
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