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The Wax Home Birth Meta-Analysis: An Outsider’s Critique

October 23rd, 2012 by avatar

Today’s post is a fascinating interview that took place between Rebecca Dekker, PhD, RN, APRN of Evidence Based Birth and Kyoung Suk Lee, PhD, MPH, RN, APRN. Rebecca asked Dr. Lee to provide a review of the Wax Home Birth Meta-Analysis, as an “unbiased outsider”, but highly skilled researcher.  Dr. Lee’s comments and critique are fascinating and provided me with many further thoughts.  Please enjoy Rebecca’s interview and share your comments. – SM

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http://www.flickr.com/photos/eyeliam/7353095052/

Shortly after starting my website, www.evidencebasedbirth.com, I had several people ask me if I could write an article about the research evidence on home birth. However, I was hesitant to do so for several reasons. Mainly, I was worried that I could not look at the evidence in an objective manner. My husband and I had recently chosen a home birth for our second child. I was worried that it would be difficult to objectively examine the research evidence on home birth, given my personal experience. The blogosphere is full of people who are strongly pro-home birth or anti-home birth, and their evaluations of the evidence are usually written through the lens of their own biases. I didn’t want to add to the plethora of biased articles already out there.

Then I had a sudden burst of inspiration. What if I asked one of my colleagues—who has no biases about childbirth—to review the home birth literature for me? In particular, I wanted to find someone who could review the Wax home birth meta-analysis (Wax, Lucas et al. 2010) and give me a fair assessment of its scientific value.

I chose the Wax meta-analysis for this review because in 2011, the American Congress of Obstetricians and Gynecologists emphasized the results of the Wax study in its official statement on home birth. Their statement said: “Women inquiring about planned home birth should be informed of its risks and benefits based on recent evidence. Specifically, they should be informed that although the absolute risk may be low, planned home birth is associated with a twofold to threefold increased risk of neonatal death when compared with planned hospital birth.”(ACOG, 2011)

Dr. Kyoung Suk Lee, PhD, MPH, RN, APRN

It did not take me long to figure out who I would ask to review the Wax study. Dr. Kyoung Suk Lee is considered by her colleagues to be a rising star in the field of cardiovascular research. She recently graduated with a PhD in Nursing, and she just accepted a job at a research university. People who work with Dr. Lee say that she is extremely intelligent, hard-working, and a future leader in her field. Dr. Lee’s expertise has been recognized with research awards from the Heart Failure Society of America, the Society for Heart-Brain Medicine, and the Cleveland Clinic Heart-Brain Institute, among others. She has published her work in nursing and cardiology journals. Furthermore, I knew that Dr. Lee did not have any biases about childbirth, home birth, or hospital birth. I asked Dr. Lee if she would be willing to review the Wax meta-analysis for me, and she kindly agreed.

What follows is my interview of her about the study and its results (RD in bold, KSL unbolded).

Do you have any biases or conflicts of interest related to home or hospital birth?

I do not have any biases related to home or hospital birth.

Could you summarize the methods and results of the Wax study?

The purpose of this meta-analysis was to compare maternal and neonatal outcomes between planned home-and hospital-births.

Using an electronic database search and bibliography search, the authors retrieved 237 articles and included 12 articles in their meta-analyses. Of 12 articles included, 3 were conducted after 2000 while 9 were conducted before 2000. Of 12 articles, 2 were conducted in the US (one was a retrospective design) while 10 were conducted outside US.

Women in the planned home birth group had better maternal outcomes than women in the planned hospital group. They had fewer interventions such as epidurals and episiotomies, and lower morbidity (infection, 3rd or 4th degree lacerations, hemorrhages, and retained placenta). There were no differences in cord prolapse between the two groups.

For neonatal outcomes, babies born to women in the planned home birth group were less likely to experience prematurity and low birth weight. However, babies born to women in the planned home birth group were more likely to experience neonatal death compared to women in hospital birth.

What is the difference between neonatal and perinatal mortality? What does this have to do with the results?

Based on the definitions given by the authors, neonatal mortality was defined as “death of live born child within 28 days of birth.” This is a subset of an overall outcome– perinatal mortality, which was defined as “stillbirth (of at least 20 weeks or 500g) or death of live born child within 28 days of birth.”

According to the authors, there were no differences in perinatal death (the overall outcome) between planned home birth and hospital birth groups. However, homebirth was associated with 2 times higher risk for neonatal death (the subset of deaths occurring 28 days after birth) in all infants and 3 times higher risk for neonatal death in infants who did not have any congenital birth defects.

Interestingly, if you look at page 243.e3, the authors did a sensitivity analysis. In this analysis, they excluded the studies that had home births that were not attended by certified midwives or certified nurse midwives. In this analysis, they found that there were no differences in neonatal deaths between the home birth and hospital birth groups. This means that in the studies in which midwives with certification of some kind attended home births, the outcomes were the same except there was no increase in the neonatal death rate. In my opinion, we have to pay attention to results of sensitivity analyses because this allows us to see the results based on studies which were definitely known to be eligible or clearly described their methods and outcomes.

What is your opinion on the scientific rigor of this meta-analysis?

One thing that was strange to me is the odds ratios (ORs) in the tables. For example, in table 2, under morbidity, the percentages of infection between home births and hospital births were 0.7 vs. 2.6 (its OR was 0.27) while percentages of perineal laceration were 42.7 vs. 37.1 (its OR was 0.66). To a researcher, these numbers don’t make sense.

Many of the studies included were older (half of the studies were conducted more than 20 years ago) so results may not reflect the current practice at home births or hospital births.

The authors did not provide detailed information on how they evaluated the quality of studies included, although they cited a paper describing the method of study evaluation. This makes it difficult if not impossible to determine whether the studies they included were of good or poor quality.

The authors mentioned that women with high risks would prefer hospital births so that it would expect that home births have better outcomes than hospital births in some maternal and neonatal outcomes. If this was a concern, I wonder why the authors didn’t just focus on only the studies that used matching methods, in order to minimize confounding factors.

What is the difference between relative risk and absolute risk, and how does that apply to women who want to have a home birth?

Absolute risk is the probability of something occurring. They may be expressed as percentages or ratios. For example, neonatal mortality rate in the United States is 2.01 per 1,000 live births. This is .201 percent (2.01/1000 = .201/100).

http://www.flickr.com/photos/mikeporcenaluk/3789756395/

Relative risk is a comparison between different risk levels, such as the neonatal mortality rate of home birth compared to the neonatal mortality rate of hospital birth. The researchers found that there was a higher relative risk in neonatal mortality at home births compared to hospital births, but the overall absolute risk for both was small.

How can women know whether the Wax study results would be applicable to their own individual situation?

Meta analysis is one way to generalize findings from different studies. However, women and clinicians should interpret these results cautiously because the studies included were very different from one another and some of the studies included may not have been of good quality. Also, it would be important to note that the overall neonatal death rate that they report reflects home births that were attended by midwives as well as those that may not have had any kind of certified midwife present.

Because this study seems to have some flaws, the conclusion is tentative. I do not know if this article has any implications for pregnant women.

What do you think is the value of asking someone with no conflicts of interest to evaluate controversial research? Does Dr. Lee’s even-handed critique make you view the results of this study any differently? How do you feel about Dr Lee’s conclusion that the study’s results are tentative, and that the Wax study might not have any implications for pregnant women? Please share your thoughts and comments with other readers.

References

(2011). “ACOG Committee Opinion No. 476: Planned home birth.” Obstetrics and gynecology 117(2 Pt 1): 425-428.

Wax, J. R., F. L. Lucas, et al. (2010). “Maternal and newborn outcomes in planned home birth vs planned hospital births: a metaanalysis.” Am J Obstet Gynecol 203(3): 243 e241-248.

About Rebecca Dekker

Rebecca Dekker, PhD, RN, APRN, is an Assistant Professor of Nursing at a research-intensive university and author of www.evidencebasedbirth.com. Rebecca’s vision is to promote evidence-based birth practices among consumers and clinicians worldwide. She publishes summaries of birth evidence using a Question and Answer style.

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When Scientific Methods Fail: New Criticisms Over the Wax et al Homebirth vs. Hospital Birth Study

April 4th, 2011 by avatar

Just when one might think the controversy over the Wax et al planned homebirth vs. planned hospital birth study might be dying down, it is instead heating up again.

The American Journal of Gynecology—in which the study was originally published in September, 2010—released its April 2011 issue last Friday, full of Letters to the Editor criticizing the study.  Written by social science, epidemiology, bioethics and public health doctoral university researchers and midwives, it almost seemed as if the journal was preparing to retract the Wax article by these inclusions.  But really, they were providing the platform for the study authors to respond to the critical letters, as suggested in an excerpt from one of those responses:

“Although our findings may be unpopular in certain quarters, they result from appropriate rigorous scientific methods that have undergone appropriate peer review.”

(More on the “scientific methods” later.)

In the concluding Editor’s comment, we are told an (anonymous) independent panel of maternal fetal medicine experts convened to review the data in the Wax study—a move to theoretically decide whether or not the journal should retract the article.  The panel’s recommendations, following this analysis of the Wax et al data, were that AJOG should publish online, a full summary of the graphs for each outcome included in the study and that no retraction of the article is warranted.  (They did admit to finding ‘minor’ discrepancies in the data—but none that seemed to warrant rescinding the article altogether.)

I will say, I have to give AJOG a little credit here:  they didn’t have to print those letters.  I can only imagine how many letters in a month a large journal like that receives.  The managing and chief editors certainly could have kept all those letters to themselves, never to print a single one.  Perhaps their PR department convinced them that doing so would have created a larger fire storm than the one (still) brewing.

Coming on the heels of articles in Nature and the Lancet, which seriously called into question the conclusions of the Wax study, there has certainly been a lot of pressure on AJOG to address its decision to publish the article at all.

Medscape is also on board the debate—having already re-published the Nature article and now making available a rebuttal article from a group of researchers—including the authors of the British Columbia and Netherlands homebirth studies the Wax article incorrectly attributed and irresponsibly excluded, respectively.  This latest article, entitled Planned Home vs. Hospital Birth: A Meta-Analysis Gone Wrong, by Carl Michal, PhD, et al, was also published last Friday.

An excerpt from the Michal paper encapsulates the problem with the Wax meta-analysis:

The statistical analysis upon which this conclusion was based was deeply flawed, containing many numerical errors, improper inclusion and exclusion of studies, mischaracterization of cited works, and logical impossibilities. In addition, the software tool used for nearly two thirds of the meta-analysis calculations contains serious errors that can dramatically underestimate confidence intervals (CIs), and this resulted in at least 1 spuriously statistically significant result. Despite the publication of statements and commentaries querying the reliability of the findings, this faulty study now forms the evidentiary basis for an American College of Obstetricians and Gynecologists Committee Opinion, meaning that its results are being presented to expectant parents as the state-of-the-art in home birth safety research.

Critical analysis of the Wax study by Michal et al includes the following:
°data included in the study suggests a higher neonatal death rate (for both home and hospital births) compared to perinatal death rates.  This, of course, is not possible as neonatal deaths ought to be included in the perinatal death numbers—therefore the data here are paradoxical in nature.

°multiple numerical errors including inconsistencies in data provided in both original and supplemental source papers; incompatibilities between data from cited sources and that which is represented in the Wax study

°inconsistencies in the authors’ definitions of perinatal and neonatal mortality

°miscalculations of some odds ratios (OR) and confidence intervals (CI)—sometimes to the tune of drastic underreporting of the CI—resulting in inaccurate statistically significant positive or negative results

°inappropriate data inclusion criteria (such as that for perineal tears, in which the Wax study only included data on first and second degree tears, rather than all perineal lacerations)

°the meta-analysis spreadsheet used to calculate 13 out of the 21 outcomes contained a computational error—making all data computed with that spreadsheet incorrect

°inclusion of reference works that, themselves, have been highly criticized for statistical inaccuracies (such as the Pang et al study that included unplanned home births when it had set out to only assess planned homebirths)

°misappropriated causation:

…the discussion of causes of neonatal mortality focuses on findings from studies that were not included in the meta-analysis, including studies that mix high-risk with low-risk cases. Of the studies that are included in the meta-analysis, none associates rates of intervention with rates of neonatal mortality.

AJOG, in an attempt to rule on the debate of whether or not the data presented in the Wax study are even valid, may have just shot itself in the foot.  Since when did ‘we published an inaccurate study, and we stand by those inaccuracies’ become acceptable?

 

(see appropriate references attached to above-linked articles)

Posted by:  Kimmelin Hull, PA, LCCE

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