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significantly overweight, and might have a wide range of disease risk factors with varying levels of severity. As researchers and clinicians, our most important criterion should be indisputable safety, and low-carbohydrate diets currently fall short of this benchmark. *Lyn M Steffen, Jennifer A Nettleton University of Minnesota School of Public Health, Division of Epidemiology and Community Health, Minneapolis, MN 55454, USA
[email protected]
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We declare that we have no conflict of interest. 1 2
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Chen TY, Smith W, Rosenstock JL, Lessnau KD. A life-threatening complication of Atkins Diet. Lancet 2006: 367: 958. Astrup A, Larsen TM, Harper A. Atkins and other low-carbohydrate diets: hoax or an effective tool for weight loss? Lancet 2004; 364: 897–99. Freedman MR, King J, Kennedy E. Popular diets: a scientific review. Obes Res 2001; 9 (suppl 1): 1S–40. Metgas CC, Barth CA. Metabolic consequences of a high dietary–protein intake in adulthood: assessment of the available evidence. J Nutr 2000; 130: 886–89.
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Foster GD, Wyatt HR, Hill JO, et al. A randomized trial of a lowcarbohydrate diet for obesity. N Engl J Med 2003; 348: 2082–90. Samaha FF, Iqbal N, Seshadri P, et al. A low-carbohydrate as compared with a low-fat diet in severe obesity. N Engl J Med 2003; 348: 2074–81. USDA. MyPyramid.gov: steps to a healthier you. http://www.mypyramid. gov/ (accessed Jan 12, 2005). Nutrition and Food Security Programme. Food-based dietary guidelines in the WHO European region. 2003: http://www.euro.who.int/ Document/E79832.pdf (accessed Jan 12, 2006). Steffen LM, Jacobs DR, Stevens J, Shahar E, Carithers T, Folsom AR. Associations of whole grain, refined grain, and fruit and vegetable consumption with all-cause mortality, incident coronary heart disease and ischemic stroke: the ARIC Study. Am J Clin Nutr 2003; 78: 383–90. Ness AR, Powles JW. Fruit and vegetables, and cardiovascular disease: a review. Int J Epidemiol 1997; 26: 1–13. Malin AS, Qi D, Shu XO, et al. Intake of fruits, vegetables and selected micronutrients in relation to the risk of breast cancer. Int J Cancer 2003; 105: 413–18. Cummings S, Parham ES, Strain GW. Position paper of the American Dietetic Association: weight management. J Am Diet Assoc 2002; 102: 1145–55. US Department of Health and Human Services, US Department of Agriculture. 2005 U.S. Dietary Guidelines for Americans. http:// www.health.gov/dietaryguidelines/dga2005/document/pdf/ dga2005.pdf (accessed Jan 11, 2006).
Systematic reviews: when is an update an update? Governments are investing heavily in the use of systematic reviews to inform health-care policy.1 The value of systematic reviews is best when they are kept up to date, since evidence is continually evolving as new research becomes available. For example, certain healthcare interventions currently known to be effective will be shown to be ineffective or harmful in the future, or vice versa.2 To ignore the emergence of new information might therefore undermine the validity of systematic reviews. Although many researchers have addressed several methodological issues of updating systematic reviews,2–6 none has provided a formal definition of what constitutes an update. The definition7 of “to update” means “to extend up to the present time” or “to include the latest information”. Without a formal definition, investigators and readers could have difficulties in determining whether or not any given systematic review has been updated. Furthermore, researchers who undertake surveys of updating practices or studies that deal with different methods of updating could perceive updating processes differently, leading to inconsistent assessments of how current any given systematic review is. These differences, in turn, will render current and future studies non-comparable. www.thelancet.com Vol 367 March 18, 2006
We believe that the introduction of a formal definition and explanation for this important construct is long overdue. We define an update of a systematic review as a discrete event with the aim to search for and identify new evidence to incorporate into a previously completed systematic review. The central and necessary element of an update is the effort to identify new evidence. We use “new evidence” broadly—evidence that has not been included in the previously completed review. For example, use of the search strategy (eg, MeSH terms, years searched) from the original review, but with an additional database (MEDLINE vs MEDLINE and EMBASE) to identify new evidence, is regarded as an update. Alternatively, updating could be initiated after a specific period of time has elapsed since the completion of the original systematic review, which allows for the identification of new evidence that has emerged during this time. Even if a search does not identify any new evidence relevant to the systematic review, we believe that this event still constitutes an update. To undertake an updating process, a systematic search needs to be initiated with the purpose of determining whether or not new evidence exists. 881
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An update can occur at any time after the completion of the original (or already updated) systematic review. For example, an update could be started immediately after the completion of a systematic review by using the same search strategy but including additional electronic databases. However, a more common practice is to update systematic reviews after a certain period has passed since the completion of the original version. Time could serve as a trigger or an indicator for the initiation of the updating process. A distinguishing feature of an updated systematic review from a new review is that during updating the originally formulated protocol (eg, eligibility criteria, search strategy) is retained, and sometimes extended, to accommodate newly identified evidence (eg, new treatment type, diagnostic method, outcome, different population). We think that a mere re-analysis or replication of the previously undertaken systematic review by use of a new or modified method (eg, statistical pooling) without the initiation of a new search (eg, extension of the sourcerelated or time-related domains not covered in the previous systematic review) is not an update. Similarly, this replication using a new search terminology (eg, MeSH terms) without an effort to identify new evidence would not be regarded as an update either. However, if the re-analysis with the new or modified method (or new MeSH terms) is combined with a new search, this procedure can be defined as an update because it is an effort to identify new evidence, according to our definition. Corrections of mistakes, errors, or typographic errors detected in a previously completed systematic review would not constitute an update, because these operations do not allow for the possibility of new evidence being identified. Apart from inconsistent use of what constitutes an update, there are other challenging issues related to updating—eg, it is not clear when to update any given systematic review.8,9 Updating that is too frequent when the pace of reported research is slow might be unnecessary and will probably result in wasted resources, whereas low updating frequency in a fast-developing specialty could render the results of systematic reviews outdated, misleading, or both.8–10 A systematic review summarising methods to indicate when and how to update systematic reviews would probably clarify any
uncertainty and also highlight existing gaps in the evidence. Finally, informative indexing of updated systematic reviews will improve when readers are alerted by the term “update” or another synonym included in review titles. The success of the Cochrane Collaboration, the Evidence-Based Practice Center programme, and other efforts has substantially increased the number of systematic reviews. If systematic reviews are to retain their validity in helping to inform the effective delivery of health care, they must be kept up to date. *David Moher, Alexander Tsertsvadze Chalmers Research Group, Children’s Hospital of Eastern Ontario Research Institute, Ottawa K1H 8L1, Ontario, Canada
[email protected] We thank the following for feedback on previous versions of our definition for updating systematic reviews: Margaret Sampson, Raymond Daniel, Nick Barrowman, Kaveh Shojania, Jessie McGowan, and Tanya Armour. We declare that we have no conflict of interest. 1
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Atkins D, Fink K, Slutsky J. Better information for better health care: the Evidence-based Practice Center Program and the Agency for Healthcare Research and Quality. Ann Intern Med 2005; 142: 1035–41. Chalmers I, Enkin M, Keirse MJNC. Preparing and updating systematic reviews of randomized controlled trials of health care. Milbank Q 1993; 71: 411–37. Chalmers I, Haynes B. Reporting, updating, and correcting systematic reviews of the effects of health care. BMJ 1994; 309: 862–65. Higgins JPT, Green S, eds. Cochrane Handbook for Systematic Reviews of Interventions 4·2·5 [updated May 2005]. In: The Cochrane Library, issue 3, 2005. Chichester, UK: John Wiley & Sons, 2005.
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Koch G. Less than half of the Cochrane Reviews are current. Proceedings of the 11th Cochrane Coloquium: evidence, health care, and culture, Oct 26–31, 2003; Barcelona, Spain. Cochrane Methodol Register 2005; 3. Higgins JPT. Prevalence and problems of updated reviews: a survey and discussion. In: Proceedings of the 2nd Symposium on Systematic Reviews: beyond the basics, January, 1999; Oxford, UK. Cochrane Methodol Register 2005; 3. Merriam-Webster’s Collegiate Dictionary, 10th edn. Springfield, Massachussetts: Merriam-Webster, 1996.
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Weller D. Managing and updating the evidence. In: Evidence-based health advice workshop, Nov 4–5, 1998; Melbourne, Australia. http://www. menziesfoundation.org.au/conferences/ebm/ebm08wel.htm (accessed Feb 16, 2006). Chapman A, Middleton P, Maddern G. Early updates of systematic reviews—a waste of resources? In: Proceedings of the 4th Symposium on Systematic Reviews: pushing the boundaries, July 2002; Oxford, UK. Cochrane Methodol Register 2005; 3. French S, McDonald S, McKenzie JE, Green S. Investing in updating: how do conclusions change when Cochrane systematic reviews are updated? BMC Med Res Methodol 2005; 5: 33.
Decision-making about caesarean delivery There is a fundamental but unrecognised flaw in current thinking about caesarean delivery. Modern obstetrics teaching dictates that a caesarean delivery is either medically indicated or not—ie, elective or on demand. Accepted indications include placenta praevia and cephalopelvic disproportion. We propose a rethinking that challenges the idea that all indications for caesarean delivery can be reliably categorised binomially. A grey area exists that has a larger effect on modern-day obstetrics than most people think. Discussion of elective caesarean delivery has been revitalised. Published work has examined the right of pregnant women to choose the mode of delivery, whether or not there is an accepted medical indication.1–3 Scientific evidence about the safety and potential benefits of elective caesarean delivery has been accumulating. Obstetricians worldwide have identified the idea of caesarean delivery on maternal request as a contemporary ethical controversy.1,4 The US National Institute of Child Health and Human Development is convening an expert consensus meeting on March 27–29, 2006, to discuss this topic.5 The issue of caesarean delivery by patient’s request is not solely limited to the antepartum period. One of every eight intrapartum caesarean deliveries has some clinical element of maternal or clinical choice.6 The time has come to fully assess the subtle, but real, factors that alter decision-making about caesarean delivery by both doctor and patient. Appropriate use of medical interventions should be based on evidence of benefits and risks. Some caesarean deliveries are clearly medically indicated—ie, cases with good evidence that caesarean delivery decreases risks to the mother and fetus compared with vaginal delivery. However, the scarcity of data that such benefits exist means increased uncertainty about the best mode of delivery. For example, for years, breech fetuses were www.thelancet.com Vol 367 March 18, 2006
routinely delivered vaginally, because this procedure was deemed safe for the fetus and mother. However, because findings have challenged the notion that vaginal breech delivery is as safe as caesarean delivery,7 most obstetricians have abandoned this breech delivery. Another example is vaginal birth after previous caesarean delivery. Although this practice became common in the 1990s and was thought to improve obstetric outcomes, evidence has pointed to the fact that there might be real, albeit rare, outcomes of such an approach, and alternatives—ie, repeat caesarean delivery—have become more acceptable.8 Two important questions arise. First, when there is real clinical uncertainty about the benefits and risks of caesarean section, how should obstetricians form their judgments? Second, how should they present the choice to the patient? Traditionally, obstetricians have based clinical judgment on beneficence—ie, the ethical obligation to do good for patients by the medically best alternative. However, beneficence-based clinical judgment is not dichotomous; it admits of justified variation when evidence lends support to more than one alternative as reasonable. How should decision-making proceed when the clinical situation proves to have more than one reasonable management option with an incremental increased risk to either the neonate or mother depending on the path chosen? Who should decide how much risk is worth taking? Should the patient be given any role in the decision-making? Traditionally, the answer to the last question has been no, other than to obtain consent to authorise the chosen clinical management. Obstetricians should engage in evidencebased decision-making with patients to implement an important implication of patients’ autonomy: when there is real uncertainty about clinical benefits and risks of reasonable alternatives, competent adult patients 883
