Planned Home vs Hospital Birth: A Meta-Analysis Gone Wrong

Carl A. Michal, PhD; Patricia A. Janssen, PhD; Saraswathi Vedam, SciD; Eileen K. Hutton, PhD; Ank de Jonge, PhD


April 01, 2011

In This Article

Numerical Errors

The results of the meta-analysis are presented in 2 tables: (1) for maternal outcomes, and (2) for neonatal outcomes.[1] For each outcome, Wax and associates provided the number of studies used in the calculation for that outcome, the number of births reporting that outcome, the total number of births in the included studies, and the summary odds ratio (OR) and 95% CI for the OR. Lists of which studies were included for each of the outcomes were not originally provided but have subsequently been made available.[8]

In attempting to reproduce some of the results, we find numerous numerical errors. In Table 2, we reproduce Wax and colleagues' table of neonatal outcomes, adding a column indicating which studies were used for each. Numerical errors are evident in every row. Many of these errors are minor, but several are highly significant, off by factors of 2 or more. In 1 instance (all perinatal deaths), the number of included studies was even incorrect. For another (large for gestational age), essentially every number is wrong.

Table 2. A Reproduction of the Neonatal Results Table

Many of the ORs and CIs have been calculated incorrectly. In some cases, this was the result of errors apparently made in the extraction of data from the original studies. For example, we point to the study of Pang and coworkers[14] from which, to obtain results found in the summary table, the investigators must have counted 13 nonanomalous neonatal deaths in the home birth group. However, from Table 4 in that paper, it is clear that only 12 deaths should have been included.

Another example of an error in data extraction is in the all neonatal deaths outcome, where, again to reproduce the results in the supplemental table, the study by Janssen and colleagues[15] must have included a neonatal death in the hospital group. The only hospital death mentioned in that report was a stillbirth, not a neonatal death.

A third example of incorrect data extraction may be found, again in the all neonatal death outcome. In the study by Koehler, Solomon, and Murphy,[13] from which Wax and coworkers apparently included no deaths, 1 of the home birth deaths fit the definition of neonatal death.

In all 3 of these cases, the studies should not have been included in these outcomes at all.

A fourth example of incorrect data extraction is found in the perineal laceration outcome for which, to reproduce the results in the summary table, the report by Janssen and colleagues[19] apparently included only first- and second-degree lacerations rather than all perineal lacerations.

Both the investigators and peer reviewers ought to have been concerned that the direction and magnitude of the ORs for a variety of outcomes were illogical. Examples include postdates, for which the occurrence frequencies of 2.1% and 2.2% make the provided OR of 1.87 seem very unlikely, and newborn ventilation, for which the frequencies of 3.7% and 4.7% similarly make the OR of 1.12 seem unlikely. Several of the denominators appearing in the tables should also have raised concerns. For example, large for gestational age and newborn ventilation both have denominators of 13,525 for the home birth groups, in the first case arising from 4 studies, but from only 3 studies in the other. The denominator 10,701 appears for hospital births for both postdates and newborn ventilation, arising from 3 studies in the first case and 4 studies in the other.


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