Anyone who has followed the discussions on Homebirth Debate knows that I have repeatedly criticized the Johnson and Davis study of homebirth, Outcomes of planned home births with certified professional midwives, because it used the wrong comparison group. Now I have found the death rate for the correct comparison group by using the same data that Johnson and Davis used.
According to Johnson and Davis, when analyzing the different intervention rates of home and hospital:
We compared medical intervention rates for the planned home births with data from birth certificates for all 3 360 868 singleton, vertex births at 37 weeks or more gestation in the United States in 2000, as reported by the National Center for Health Statistics [Births: final data for 2000. National vital statistics reports. Martin JA, Hamilton BE, Ventura SJ, Mencaker F, Park MM. Hyattsville, MD: National Center for Health Statistics, 2002;50(5)]When analyzing the different mortality rate of home and hospital, Johnson and Davis used a group derived from out of date homebirth studies. I have always thought that was strange. Why not use the neonatal mortality data of the group that served as the comparison for interventions?
I went back and looked at the neonatal mortality data for this group, the EXACT group that Johnson and Daviss felt was the perfect comparison for intervention rates. I did this by reviewing the exact same paper that Johnson and Daviss used. The paper is 105 pages long and has been divided into subsets for ease of research. The subset on neonatal mortality is Infant Mortality Statistics from the 2000 Period Linked Birth/Infant Death Data Set. Looking at the raw data we find:
2,824,196 births to white women at term (37+ weeks), see Table 2
2,602 deaths of white babies weighing more that 2500 gm see Table 6
a death rate of 0.9/1000.
The hospital neonatal death rate for white babies at term of 0.9/1000 is not corrected for congenital anomalies, pre-existing medical conditions, pregnancy complications or multiple births. The true rate is substantially lower. Nonetheless, we can make an important comparison. Johnson and Daviss reported a neonatal death rate at homebirth of 2.7/1000 (uncorrected for congenital anomalies, breech or twins). The neonatal death rate in the comparison group THAT THEY USED was less than 0.9/1000.
So now we have an explanation for why Johnson and Daviss used two different comparison groups. They used one group (births in the year 2000) for comparing medical interventions. The neonatal death rate in that exact group was 0.9/1000, half the rate of neonatal deaths at homebirth. They supressed that information by using an entirely different group (drawn primarily from the 1970's and 1980's) instead of using the death rate from the year 2000.
This piece first appeared on Homebirth Debate in January 2007.