Friday, December 15, 2006

Where we stand

I have consistently maintained that there is no scientific evidence that shows homebirth to be as safe as hospital birth. Virtually every study done to date shows an excess rate of preventable neonatal deaths in the range of 1-2/1000. There are a number of studies that CLAIM to show that homebirth is as safe as hospital birth, but they do not. Even homebirth advocates recognize that papers such as the Farm study demonstrate nothing about homebirth, and they don't argue the point any longer. When pressed, they ultimately retreat to only two or three papers, recognizing that the others are not defensible.

The paper that is cited most often is the Johnson and Daviss paper Outcomes of planned home births with certified professional midwives: large prospective study in North America published in the BMJ in June of 2005. This paper has the fewest methodological problems of any pro-homebirth paper. Nonethess, it still has methodological problems so serious as to render the conclusions of the paper invalid. As I have described many times, Johnson and Daviss used the wrong group of women to compare to the homebirth group. Instead of using low risk white women who gave birth in the hospital during the same year, they compare homebirth in 2000 to data in other people's studies from the years 1969-1991 (predominantly papers from the late 1970's and early 1980's). This is completely unacceptable for several reasons:

1. Since the neonatal death rate at hospital birth dropped consistently from 1969 -2000. Therefore, neonatal death rates prior to 2000 were higher than they were in 2000. Johnson and Daviss tried to compare the homebirth death rate in 2000 with the hospital birth death rate from approximately 25 years earlier!

2. You cannot compare data in one paper to an amalgamation of data derived from disparate papers done by other people. Johnson and Daviss actually acknowledge this in their paper, writing: "Direct comparison of relative mortality between individual studies is ill advised, as many rates are unstable because of small numbers of deaths, study designs may differ (retrospective versus prospective, assessment and definition of low risk, etc.), the ability to capture and extract late neonatal mortality differs between studies, and significant differences may exist in populations studied with respect to factors such as socioeconomic status, distribution of parity, and risk screening criteria used." Then they promptly ignore their own explanation of why such comparisons cannot be valid, and proceed to make the comparison.

3. At the time the Johnson and Daviss paper was written, the US government had already published statistics for births in the year 2000. These statistics are quite detailed, and are broken down in a variety of ways (by cause of death, by race, by state, etc). The appropriate comparison group for homebirth in 2000 is hospital birth in 2000. That data was publicly available at the time Johnson and Daviss wrote their paper. That data shows that the neonatal death rate in the hospital in 2000 was substantially lower than the neonatal death rate at homebirth in 2000.

I have been talking about this issue for months, but it has only recently started to gain traction in the homebirth community. Several interesting things have happened in the last few days.

1. I posted this critique on the Lamaze website. The first response, from Judith Lothian, was rather vague, and unsupported by any evidence. Henci Goer wrote a more detailed response which did not address at all the main point of the critique. Two days ago I posted a direct question to Henci Goer: the comparison group in the Johnson and Daviss is inappropriate, yes or no? To their credit, Lamaze did not remove the post. Thusfar they have not answered it either, despite the fact that it is a very simple question. I believe I know why; they are aware that the comparison group is inappropriate.

2. One of the posters on this site who has vociferously defended homebirth recently revealed that she teaches statistics on the college level. I asked her the same question I asked Henci Goer. She has posted multiple responses that attempted to duck the issue. Now that I have asked her to answer just one question: is the comparison group inappropriate? Thusfar she has declined to answer. I believe I know why; she knows that what Johnson and Daviss did is not a defensible statistical analysis.

3. An associate of Johnson and Daviss posted on this website yesterday, apparently at the behest of Dr. Johnson. He has invited me to write him privately. I much prefer to have this debate in public and would value the opportunity to read his defense of his statistical methods. I'm a little confused as to why he is asking me to write to him; he could easily write to me. My e-mail address is posted prominently on the site.

In addition, Ms. Haas, Dr. Johnson's associate, suggested that I submit a rapid response letter to the BMJ. This is also confusing to me. Rapid response letters, as the name suggests, are published immediately after the release of the article. The rapid responses for the Johnson and Daviss article ended back in August of 2005. It is much too late to submit a rapid response now.

In summary, I have no doubt that the comparison group used by Johnson and Daviss was inappropriate and that, therefore, the conclusion that homebirth is as safe as hospital birth is invalid. The events of the last few days suggest to me that knowledgeable homebirth supporters know this, too.


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