April 4, 2012
Volume 7 - Issue 14    

DynaMed Weekly Update

For the week ending March 30, 2012 

Last week 627 articles were evaluated via DynaMed's Systematic Literature Surveillance and 291 were added to DynaMed content.   


Based on the editors' criteria of selecting "articles most likely to change clinical practice," one article of significant interest was selected for the DynaMed Weekly Update.
Feature Article

Trial of Vaginal Birth after Cesarean May Increase Risk of Maternal Hemorrhage and Might Increase Risk of Cord Blood Markers of Neonatal Asphyxia


Expectant mothers who have had a previous cesarean delivery may choose a repeat cesarean for the subsequent birth or they may elect trial of vaginal birth after cesarean (VBAC). In population-wide, retrospective cohort study, VBAC was associated with small but significant increases in absolute risk of perinatal death and uterine rupture compared to repeat cesarean (JAMA 2002 May 22-29;287(20):2684). That and other retrospective analyses have been criticized for failing to include truly comparable groups in which all women were eligible for VBAC. Few prospective studies comparing the 2 approaches have been conducted. A new study prospectively compared planned VBAC to planned repeat cesarean in a cohort of 2,345 pregnant women (mean age 31 years) with 1 previous cesarean delivery who were all eligible for VBAC at term.


Women were assigned by patient preference to either VBAC (52.7%) or repeat cesarean. Additionally, 22 women who expressed no preference were randomized to 1 of the 2 approaches. Mean gestational age at study entry was 37.5 weeks. VBAC was successful in 43% of the women in that group. The rest had cesarean delivery (97% of the cesarean group had cesarean delivery).


The assigned and randomized groups were combined for primary analyses. The risk of major maternal hemorrhage (defined as blood loss > 1500 ml or need for transfusion) was significantly increased in the VBAC group (2.3% vs. 0.8%, p = 0.011, NNH 67) (level 3 [lacking direct] evidence). There were no significant differences in any other maternal outcomes.


For the infants, serious neonatal morbidity was defined as a composite of clinical and nonclinical outcomes including birth trauma, seizures, Apgar score ≤ 4 at 5 minutes, and other adverse events. This outcome occurred in 2.3% of the VBAC group and 0.9% of the planned cesarean group (p = 0.014, NNH 72). However, no individual components of the composite showed significant differences. The increase associated with VBAC was due primarily to trends toward increased risk for 2 markers of neonatal asphyxia: cord blood base deficit ≥ 12 mmol/L (p = 0.06) and cord pH < 7 (p = 0.13) (level 3 [lacking direct] evidence). Serious clinical outcomes were too rare for a study of this size to either demonstrate or exclude clinically important differences. There were no significant differences in perinatal death (0.2% vs. 0%). No adverse outcomes were reported in any of the randomized patients (PLoS Med 2012 Mar;9(3):e1001192).


Although cohort studies are more prone to bias than randomized trials, the small but significant differences found in this study may be of value to clinicians when advising women on their birth options. Given that only 0.94% of women had no preference and agreed to be randomized, it may be difficult to reach a definitive answer to the question of absolute risk with VBAC from a randomized controlled trial.


For more information, see the Trial of vaginal birth after cesarean (VBAC) topic in DynaMed.

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DynaMed Extra

American College of Chest Physicians (ACCP) guidelines on antithrombotic and thrombolytic therapy integrated into DynaMed


The ninth edition of the ACCP guidelines on antithrombotic and thrombolytic therapy were published in February, 2012. A new DynaMed topic, American College of Chest Physicians (ACCP) guidelines on antithrombotic and thrombolytic therapy, provides a complete summary of the guidelines, and new information has been fully integrated into 124 corresponding DynaMed topics. Some of the significant changes from the eight edition include new recommendations on diagnosing deep vein thrombosis and a new recommendation to use dabigatran instead of adjusted dose warfarin for stroke prophylaxis in patients with nonrheumatic atrial fibrillation. A complete table of contents is available in Chest 2012 Feb;141(2 suppl):1S-e801S.  

DynaMed Events
American College of Physicians (ACP) Conference
Please stop by the DynaMed booth (#1517) at the ACP Conference April 19th through the 21st. It's a great opportunity to give feedback, offer content suggestions, and explore collaboration opportunities.

Learn more about EBM and scholarly activity at seminars and education sessions at the STFM Annual Spring Conference April 25th through the 29th.

Saturday, April 28

S41: 10:30-12:00; Engaging Scholarly Activity: Electronic Peer Review of Evidence William Cayley Jr, MD; Brian Alper, MD, MSPH; Michael Mendoza, MD, MPH; Susan Hadley, MD

S43: 1:45-3:15; Using Electronic Knowledge Resources at the Point of Precepting William Cayley Jr, MD; Michael Mendoza, MD, MPH; Ingrid Watkins, MD; Mathew Devine, DO; Alexander Chessman, MD 



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About DynaMed Weekly Update

Prepared by the clinician members of the DynaMed Editorial Team, DynaMed Weekly Update is a compilation of one to five articles selected from DynaMed's Systematic Literature Surveillance as articles most likely to change clinical practice.

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CME Information


0.25 AMA PRA Category I Credit(s)™
Family Physicians: 0.25 Prescribed credits
Nurse Practitioners: 0.25 Contact hours
Release Date: April 4, 2012 
Expiration Date: April 4, 2013
Estimated Completion Time:
15 minutes
There is no fee for this activity.

To Receive Credit 
In order to receive your certificate of participation, you should read the information about this activity, including the disclosure statements, review the entire activity, take the post-test, and complete the evaluation form. You may then follow the directions to print your certificate of participation. To begin, click the CME icon at the end of the article.

Program Overview

Learning Objectives

Upon successful completion of this educational program, the reader should be able to:
1. Discuss the significance of this article as it relates to your clinical practice.
2. Be able to apply this knowledge to your patient's diagnosis, treatment and management.
Faculty Information
Alan Ehrlich, MD - Assistant Clinical Professor in Family Medicine, University of Massachusetts Medical School, Worcester, Massachusetts, USA; Deputy Editor, DynaMed, Ipswich, Massachusetts, USA

Michael Fleming, MD, FAAFP - Assistant Clinical Professor of Family Medicine and Comprehensive Care, LSU Health Science Center School of Medicine, Shreveport, Louisiana, USA; Assistant Clinical Professor of Family Medicine, Department of Family and Community Medicine, Tulane University Medical School, New Orleans, Louisiana, USA; Chief Medical Officer, Amedisys, Inc. & Antidote Education Company

Dr. Ehrlich, Dr. Fleming, DynaMed Editorial Team members, and the staff of Antidote Education Company have disclosed that they have no relevant financial relationships or conflicts of interest with commercial interests related directly or indirectly to this educational activity.
No commercial support has been received for this activity.

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AAFP: This activity, DynaMed Weekly Update 2011, has been reviewed and is acceptable for up to 13 Prescribed credits by the American Academy of Family Physicians. AAFP accreditation begins March 2, 2011. Term of approval is for one year from this date. Each Weekly Update is approved for 0.25 Prescribed credits. Credit may be claimed for one year from the date of each Weekly Update.


AANP: This program is approved for 0.25 contact hour of continuing education by the American Academy of Nurse Practitioners.  

Program ID 1102072E.

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