Ultrasound Obstet Gynecol 2002; 19: 327– 328
Opinion
Blackwell Science, Ltd
Routine ultrasound for the prenatal diagnosis of congenital diaphragmatic hernia: the ‘isms’
This issue of the Journal sees the publication of the latest in the very productive Euroscan study group series1. This international, multicenter, prospective study involving 20 centers from 12 European countries examines the sensitivity of prenatal ultrasound in the detection of congenital diaphragmatic hernia. The study mixes data from both population and hospital registries of over 700 000 deliveries, and even includes some centers where ultrasound is not performed routinely in pregnancy. The data revealed a population prevalence of 2.6 per 10 000 births, with an overall sensitivity of 59%, for congenital diaphragmatic hernia. The authors conclude that prenatal detection rates have improved in the last decade but still vary greatly between study centers, possibly due to differences in skill and technology. Additional findings were that the mean gestational age of diagnosis is 24 weeks (later than the routine scan) and that the presence of associated malformations increases the detection rate. The findings of this study regarding the prenatal diagnosis of congenital diaphragmatic hernia deserve a more detailed analysis. There are several different possible attitudes one can adopt when it comes to the role of routine ultrasound screening in obstetrics.
CRITICISM Ensuring uniformity of data collection is one of the major problems with multicenter, multinational collaborations. One previous study of over 700 000 pregnancies carried out in the state of California, reported a prevalence of 3.3 per 10 000 live births for congenital diaphragmatic hernia when ascertained by a standardized population-based birth defects monitoring program2. Although the overall prevalence of the Euroscan study was within the expected range (2.6/10 000), the individual unit prevalence varied from as low as 0.4/ 10 000 (North-east Italy) to 7.3/10 000 (Mainz). It is unlikely to be a coincidence that North-east Italy with the lowest prevalence had the most patients (111719) and that Mainz with the highest prevalence was one of the lowest in terms of patient numbers (9535). The low prevalence is easily explained by poor study ascertainment from missed postnatal diagnosis or declined postmortems. In contrast, high prevalence is likely to be a consequence of referral bias or, more worryingly and less plausibly, a real rise in the congenital malformation rate. With such differences in ascertainment, it is not surprising that the sensitivity for the prenatal diagnosis varied from as low as 29% (Lithuania) to as high as 100%. Units with a low prevalence are likely to have higher sensitivities, because the cases that were undiagnosed on prenatal ultrasound continued
OPINION
undetected after delivery. Higher sensitivities would also be expected in units with only a few cases (Barcelona and El Valles) or in tertiary centers, such as in Paris, with high prevalence possibly due to referrals (5.4/10 000).
SKEP T ICISM This study has failed to demonstrate any benefit from routine ultrasound screening for congenital diaphragmatic hernia. Indeed, the antenatal detection rate in countries that do not have a policy of offering routine prenatal screening (58%) was found to be similar to the overall sensitivity of ultrasound (59%). It would seem that a policy of targeted antenatal ultrasound screening for clinical indications is as effective as routine ultrasound screening. Additionally, the authors reiterate the statement that studies are yet to demonstrate that prenatal diagnosis would confer a significant benefit to neonates born with congenital diaphragmatic hernia3. The data also support previous contentions that routine ultrasound screening is more likely to detect fetuses with multiple abnormalities and/or chromosomal defects, for which the prognosis is invariably poor. Other studies also seem to suggest that the cases that are missed on ultrasound or diagnosed late in pregnancy have a better neonatal outcome4.
REALISM The study attributes poor prenatal detection rates to differences in skills and technology. In fact, the only authors to retrospectively study reasons for failed detection demonstrated that, in a third of cases, obvious ultrasound features were not recognized and, in two thirds of cases, the ultrasound examination was suboptimal, with the standard views not being obtained5. None of the cases in the latter study were missed because the defect was too small to be diagnosed in the second trimester, questioning the previously held premise that small, good-prognosis defects are often missed at the midtrimester scan. Indeed, since the first small-scale report to show improvement in neonatal outcome with third-trimester diagnosis4, subsequent, much larger studies have failed to confirm this finding6,7. The reason for this discrepancy appears to be related to whether the data were analyzed including or excluding cases with multiple fetal abnormalities. The ultimate question seems to be: does prenatal diagnosis really improve neonatal outcome? It would be churlish to suppose that prior knowledge of a congenital defect is of no value. This may be the case if we measure the quality of health care purely by survival, rather than other less measurable factors such as parental choice, information and preparation, as
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Opinion well as optimal utilization of health care resources. Should we require definitive evidence that prenatal ultrasound results in significant improvement in neonatal survival, then a randomized, blinded study of revealed and concealed prenatal diagnosis would be required. Such a study is ultimately totally impractical and would take the realms of evidencebased practice to unrealistic lengths. The realization of the benefits of antenatal ultrasound screening will only occur once training of sonographers and audit of outcomes are made a mandatory part of clinical practice. Few other screening programs would have such universal uptake without recourse to some standardization of technique, audit of outcomes and external quality assurance. Identification of situs solitus, cardiac axis deviation and the stomach bubble should be a standard part of any secondtrimester ultrasound examination. Ultrasound is a targetoriented real-time investigation. As such, the responsibility for making the diagnosis and reporting on the investigation should lie firmly with the practitioner carrying out the realtime investigation rather than the physician reviewing still images after the fact. This may well present greater difficulties in countries where the latter is the norm.
FUTURISM The role of extracorporeal membrane oxygenation in the management of neonates with congenital diaphragmatic hernia has been debated for over a decade. From being heralded as the panacea for this condition, this technique has finally settled into its true role as a temporary support strategy for the more severely affected neonates8. Within the latter context, it seems to improve the likelihood of survival, but with a discernable increase in the risk of physical and neurological morbidity in the survivors. A more exciting but still emergent therapy is that of fetal tracheal occlusion. This technique is supposed to promote fetal lung maturation, thereby decreasing the risk of pulmonary hypoplasia, the major cause of neonatal mortality. Both open fetal surgery and endoscopic techniques have been used to carry out this procedure, and tracheal occlusion has been achieved either by external clipping or the use of intratracheal
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Thilaganathan occlusion devices. Although permanent tracheal occlusion will require Cesarean section delivery and the EXIT (ex-utero intrapartum treatment) procedure, a number of temporary occlusive devices are being developed which should make this avoidable. The awarding of a recent National Institute of Health grant to support a randomized study of conventional management vs. fetoscopic tracheal occlusion heralds a new dawn in the advancement of fetal therapy9. B. Thilaganathan* *Fetal Medicine Unit, Academic Department of Obstetrics and Gynaecology, St. George’s Hospital Medical School, Cranmer Terrace, London SW17 0QT, UK (e-mail:
[email protected])
REFERENCES 1 Garne E, Haeusler M, Barisic I, Gjergja R, Stoll C, Clementi M and The Euroscan Study Group. Congenital diaphragmatic hernia: evaluation of prenatal diagnosis in 20 European regions. Ultrasound Obstet Gynecol 2002; 19: 329–33 2 Torfs CP, Curry CJ, Bateson TF, Honore LH. A population-based study of congenital diaphragmatic hernia. Teratology 1992; 46: 555– 65 3 Skari H, Bjornland K, Haugen G, Egeland T, Emblem R. Congenital diaphragmatic hernia; a meta-analysis of mortality factors. J Pediatr Surg 2000; 35: 1187– 97 4 Bronshtein M, Lewitt N, Sujov PO, Makhoul IR, Blazer S. Prenatal diagnosis of congenital diaphragmatic hernia: timing of visceral herniation and outcome. Prenat Diagn 1995; 15: 695– 8 5 Lewis DA, Reickert C, Bowerman R, Hirschl RB. Prenatal ultrasonography frequently fails to diagnose congenital diaphragmatic hernia. J Pediatr Surg 1997; 32: 352– 6 6 Wilson JM, Fauza DO, Lund DP, Benacerraf BR, Hendren WH. Antenatal diagnosis of isolated congenital diaphragmatic hernia is not an indicator of outcome. J Pediatr Surg 1994; 29: 815– 9 7 Steinhorn RH, Kriesmer PJ, Green TP, McKay CJ, Payne NR. Congenital diaphragmatic hernia in Minnesota. Impact of antenatal diagnosis on survival. Arch Pediatr Adolesc Med 1994; 148: 626 –31 8 The Congenital Diaphragmatic Hernia Study Group. Does extracorporeal membrane oxygenation improve survival in neonates with congenital diaphragmatic hernia? J Pediatr Surg 1999; 34: 720 –4 9 http://www.fetus.ucsf.edu/ ftc/innovations/ grant.html
Ultrasound in Obstetrics and Gynecology
