Much Ado About a Meta-Analysis (On Home vs. Hospital Birth)

July 16, 2010

A recently published meta-analysis* by Joseph Wax and others in the American Journal of Obstetrics and Gynecology has caused quite a stir, primarily because of the authors’ conclusion that “Less medical intervention during planned home birth is associated with a tripling of the neonatal mortality rate.” As we’ll see, things aren’t quite so simple on a closer look.

Upon reading the Wax paper, my first response was “Great, I’m going to have to read every one of the original studies to make heads or tails of this.” This is because, as Amy Romano points out when she notes the absence of forest plots (which would provide more detail on the findings of each included study, and are common among this type of paper), the meta-analysis itself is not terribly detailed* with regards to the characteristics and findings of each included study.

Likewise, it was difficult (for me anyway, perhaps someone else can chime in) to make some of the numbers add up, such as the size of the planned home birth population analyzed for neonatal deaths, and here again I feel the need to revisit each of the original studies in order to better understand the possible meaning for home birth safety.

First, the authors emphasize the conclusion that less frequent intervention is “associated with” increased neonatal death. The term “associated with” implies a statistical relationship between the two factors, but as we read further we find that other variables (such as attendant type) may play a role.

As far as I can tell, the authors did not attempt to do any calculations that would specifically tie the neonatal death rate to the decreased rate of interventions (more on this in a minute), they just find that both occurred. It may be the case that some of the neonatal deaths could have been prevented in the presence of additional interventions, but this is difficult to determine based on the paper at hand.

I also would have liked to have seen more thorough explanation of what the contrast between the perinatal deaths and the neonatal deaths might mean. Perinatal death (for which the authors report no significant difference between planned home and hospital births) is defined by the authors as stillbirth of at least 20 weeks gestation or 500g through death of a live born infant up to 28 days after birth. Neonatal death (which the author reports as elevated in the planned home birth group) is defined as death up to 28 days after delivery.

So, the elevated risk of death is among live born infants up to 28 days after delivery, but it’s hard to tell how many deaths occurred during labor/delivery or in the first few days after birth (for which we might assume a more important role for intrapartum care, such as a failure to note distress or a failure to resuscitate) versus how many occurred later, or their causes or possible prevention strategies.

Without seeing more data from the original studies on the causes and time frames of the deaths, it’s difficult to fully understand any possible implications of this finding.

The authors do say in the “Comment” section (not where you’d normally expect to find results) that “planned home births were characterized by a greater proportion of deaths attributed to respiratory distress and failed resuscitation” and refer to some of the included studies for support, but I would love to see some data extracted and presented more clearly in the meta-analysis. There were very small numbers of neonatal deaths in the referenced studies, and it’s not clear from spot-checking a couple of the original papers whether those researchers actually attributed the deaths to a lack of intervention without other confounding factors.

I’m also not entirely sure how useful it is to do a meta-analysis on home vs. hospital birth using data from lots of (Western) countries when the mostly non-U.S. countries have a range of current practices/trends in home birth and midwifery (such as different standards for midwifery education and stronger traditions of home birth, etc.), and rather different healthcare systems.

I recognize that this is going to be an issue for other meta-analyses on birth topics, and I’d be interested in being pointed to any good discussions of this particular issue or in hearing others’ take in the comments.

The authors raise one other issue related to the neonatal death rate that is different from the “less intervention” conclusion — they note that when the analysis excluded studies in which the providers were not “certified or certified nurse midwives,” the odds ratios for all neonatal death and “nonanomalous” (without congenital issues) neonatal death became non-significant.

In other words, when the planned home births had some type of certified midwife present, the neonatal death rate was no different than that in the planned hospital birth group. Readers, however, must have access to the full text of the article in order to view this conclusion, which is not emphasized in the abstract or media coverage of the paper.

The authors do not provide much further definition or discussion of the attendant issue, leaving us without (again, without rereading each paper) a clear understanding of whether the neonatal deaths might have occurred in unattended/unplanned home births and/or births with some other form of attendant, or how the rate of interventions varied by type of attendant.

The Pang study, for example, contributed a large chunk of the population analyzed for neonatal deaths, but has been widely debated and criticized for including unplanned home births in its analysis of neonatal death at home birth, so further review of the methods of each study may be warranted.

The authors chose to clearly associate low rates of intervention with neonatal death, but I wonder if they would also be willing to support a statement that “lower rates of medical intervention during planned home birth is not associated with increased neonatal mortality when attended by a certified or certified nurse midwife.”

There is possibly a discussion to be had about whether different types of non-certified attendants (especially those cases with unattended or unplanned home births) had all of the sometimes necessary interventions and techniques at their disposal, but the Wax analysis does not attempt to delve into this issue.

There is some discussion of the inclusion of unplanned home births in a letter from Janssen and Klein and a reply letter from Wax, for those who have access to the journal. In the reply, Wax stands by the conclusions based on their exclusion of premature births (which they expect will reduce the number of included unplanned home births), but also notes that “In addition, the purpose of our article, as clearly stated, was to evaluate morbidity, not mortality.” Mortality, however, seems to be the prime area of interest in and focus on the article, and is a clear point of emphasis in the authors’ abstract.

Ultimately, I don’t think this meta-analysis would have warranted much attention at all if it were not for the authors’ bold statement of association between decreased rates of intervention at home birth and tripled odds of neonatal death. Without that bit of provocation through the authors’ framing (and relative lack of emphasis on the difference having a midwife attendant made, or the low absolute risk of neonatal death), I don’t think most readers would have thought much of this paper or considered it to make much of an impact on knowledge in the field.

Given the small number of included studies, readers interested in better understanding safety data on home birth are probably better off getting copies of the papers Wax refers to in the analysis, and looking at each one for its relevance.

Meanwhile, Medscape is offering CME (continuing education credits required for physicians) on the topic, under the headline, “Less Medical Intervention for Home Birth Linked to Increased Neonatal Mortality Rate.” The actual text of the CME activity is more balanced in pointing out some factors we would consider positive about home birth (such as-wait for it-some of the decreased intervention rates), but it ultimately emphasizes the point that “Currently, the American College of Obstetricians and Gynecologists does not support home birth because of safety concerns and lack of scientific study.”

We, on the other hand, would emphasize the need for clearly reported, well-conducted studies, support for women’s autonomy and informed decision-making in choosing a place of birth, and systems of care that provide the best possible outcomes for women who do choose to give birth at home.

*For more information on the kind of information you should expect to see in a meta-analysis, see PRISMA statement, a set of guidelines for reporting meta-analyses and systematic reviews.

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