Correspondence
Re: Consensus definition for placental fetal growth restriction: a Delphi procedure Gordijn et al.1 aim to establish definitions for placental fetal growth restriction (FGR). We agree with their statement that, from both a clinical and a scientific perspective, it is most relevant to distinguish between fetuses with FGR that are at risk for adverse outcomes and fetuses that are physiologically small-for-gestational age. We are, however, concerned that this aim cannot be reached by consensus definitions for placental FGR established through a Delphi procedure. A Delphi procedure – as the authors themselves explain – is an instrument with which to reach consensus on, for example, research questions that cannot be answered with empirical evidence and complete certainty2 . Since empirical evidence can be obtained on this subject, we question the use of consensus to establish these definitions as the optimal procedure. While diagnosis and prognosis are important in themselves, the most important aim of medicine is to improve outcome through intervention. For pregnancies complicated by FGR this usually concerns the decision as to whether to deliver the baby. Thus, we need accuracy studies that establish and compare the diagnostic and prognostic capacity of tests for the diagnosis of both FGR and its complications, including fetal asphyxia and even stillbirth. Subsequently, the most promising tests should be evaluated further in randomized controlled trials prior to their implementation in clinical practice. In our opinion, the Delphi consensus process bears the risk of setting standards based on opinion and experience, rather than on clinical facts. For example, the cerebroplacental ratio (CPR) is part of the authors’ definition of late FGR (i.e. gestational age > 32 weeks), although the number of studies investigating CPR in this period of gestation is very limited and its clinical value has never been assessed in randomized controlled trials3 . Furthermore, a specific cut-off value is advocated (CPR < 5th percentile), despite the fact that it is unclear which cut-off value on which CPR reference curve is optimal to reach maximum test accuracy3 . Also, uterine artery Doppler is incorporated into their Delphi consensus, although its sensitivity was shown to be as low as 26% for adverse perinatal outcome in a meta-analysis involving 4513 patients4 . By including these measurements in the diagnosis of FGR, as suggested in the Delphi consensus1 , additional Doppler ultrasound measurements (uterine artery in early FGR and middle cerebral artery in late FGR) would be indicated in over 10% of pregnant women, which would have a large impact on clinical practice. These examples underscore the need for careful assessment of the available observational studies, particularly those with minimal bias, to define which tests have good prognostic accuracy and are therefore (ethically) acceptable for further evaluation in randomized comparisons, in order to determine clinical practice. We believe that
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expert opinion bears the risk of introducing new tests without proper prior clinical evaluation. C. A. Schreurs*†, B. W. J. Mol‡§ and M. A. de Boer† †Department of Obstetrics and Gynecology, Vrije University Medical Centre, Amsterdam, The Netherlands; ‡Department of Obstetrics and Gynecology, The Robinson Institute, School of Paediatrics and Reproductive Health, University of Adelaide, Adelaide, Australia; §The South Australian Health and Medical Research Institute, Adelaide, Australia *Correspondence. (e-mail:
[email protected]) DOI: 10.1002/uog.17321
References 1. Gordijn SJ, Beune IM, Thilaganathan B, Papageorghiou A, Baschat AA, Baker PN, Silver RM, Wynia K, Ganzevoort W. Consensus definition for placental fetal growth restriction: a Delphi procedure. Ultrasound Obstet Gynecol 2016; 48: 333–339. 2. Hsu CC, Sandford BA. The Delphi Technique: Making Sense Of Consensus. Practical Assessment, Research and Evaluation 2007; 12: 1–8. 3. DeVore GR. The importance of the cerebroplacental ratio in the evaluation of fetal well-being in SGA and AGA fetuses. Am J Obstet Gynecol 2015; 213: 5–15. 4. Velauthar L, Plana MN, Kalidindi M, Zamora J, Thilaganathan B, Illanes SE, Khan KS, Aquilina J, Thangaratinam S. First-trimester uterine artery Doppler and adverse pregnancy outcome: a meta-analysis involving 55,974 women. Ultrasound Obstet Gynecol 2014; 43: 500–507.
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