COMMENTARY

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

Disclosures

April 01, 2011

In This Article

Selective and Mistaken Inclusion/Exclusion

A number of errors are apparent in the inclusion of studies. The inclusion of de Jonge and associates[17] in the all perinatal death statistic is erroneous, because that article plainly states that all children with congenital abnormalities were excluded. This study should not have been included in nonanomalous perinatal death statistics either, because the statistics provided include only intrapartum and neonatal deaths up to 7 days. This time period is strikingly different from Wax and colleagues' definition of perinatal death. This study, which contributes more than 95% of the births used for the perinatal death rates, therefore, does not provide data that are compatible with Wax and colleagues' definitions for those outcomes. It is unclear why Wax and colleagues chose to exclude this study from the calculations for neonatal mortality but include the study for perinatal mortality. If that study were removed from the calculations for the 2 outcomes for which it was erroneously included, the total number of births included in the meta-analysis would have been reduced from nearly 550,000 to just 65,000. This dramatic reduction in the size of the dataset would have significantly reduced the impact of any findings of the meta-analysis. On the other hand, if Wax and colleagues had defined perinatal death and neonatal death according to definitions used by de Jonge and associates,[17] the conclusions for these outcomes would have been quite different.

In addition, a statement in the text cites 6 of the studies[9,11,13,14,15,18] as examining neonatal deaths. This appears to mischaracterize 3[9,13,15] of these articles. One of these[15]makes clear that it does not provide neonatal death rates compatible with the authors' definition (see the footnote to Table 5 in that paper). This paper should not have been cited at this point in the text and should not have been included in the calculation.

The list of studies used for the nonanomalous neonatal death outcome included 6 of the 7 references from the all neonatal death outcome, dropping only the study by Janssen and colleagues.[15] It is truly remarkable that the Janssen study was included in the all neonatal death outcome rather than the nonanomalous neonatal death outcome, because it specifically excluded births of infants with congenital anomalies. This study was also included in the all perinatal death outcome, where, in addition to the fact that it excluded infants with congenital anomalies, the death statistics provided are incompatible with Wax's definition of perinatal death.

It appears that the study by Ackermann-Liebrich and colleagues[9] should not have been included in the neonatal death outcomes, because deaths reported in this study are referred to as perinatal death rates rather than neonatal death rates, and perinatal was not defined in that work. The study by Koehler and colleagues[13]similarly reports perinatal deaths (undefined) rather than neonatal deaths. Definitions of perinatal death vary dramatically. In fact in the United States, the National Vital Statistics Reports provide data using 2 different definitions of perinatal death rates:

  • Definition 1: infant deaths of < 7 days and fetal deaths > 28 weeks; and

  • Definition 2: infant deaths of < 28 days and fetal deaths > 20 weeks).

In 2005, these 2 rates differed by a factor of 1.6 (6.64 vs 10.73 per 1000).[21]

The paper by Pang and coworkers,[14] on the other hand, presents a completely different problem for inclusion. This article, which alone provides more than half of the neonatal deaths but just one third of the births, suffers from a number of serious flaws and has been thoroughly critiqued elsewhere.[22] One principal flaw is that it includes an unknown number of unplanned home births. Pang and colleagues[14] acknowledge this limitation of their study, and mention that previous studies show that neonatal mortality among unplanned home births is high, 73-120 per 1000 live births.

Pang and colleagues attempted to reduce the inclusion of unplanned home births by limiting data to uncomplicated pregnancies and deliveries of > 34 weeks' gestation with a midwife, nurse, or physician listed as attendant or certifier on the birth certificate. These criteria are an unreliable proxy for the true planning status; unplanned low-risk births would have been included by Pang and colleagues' criteria because many unplanned home births would have a physician, nurse attendant, or certifier.[22] According to Wax and colleagues, "An estimated 75% of low-risk singleton home births appear to be planned home deliveries."[1] This statement implies that about 25% of low-risk singleton home births in the United States are unplanned. One would expect then that as many as 1500 of the 6133 home births reported by Pang and colleagues[14] could have been unplanned. A further indication that unplanned home births are included in the study by Pang and colleagues is the fact that 7.6% of home births in that study were reported as having been attended by physicians, yet during the study period not a single physician in Washington state was known to offer home birth services.[22] Given that Wax and colleagues' stated goal is to compare outcomes of planned home vs planned hospital births, it is extraordinary and incomprehensible that the study by Pang and colleagues was included.

In summary, at least 4[9,13,14,15] of the 7 studies used to calculate the neonatal death outcomes appear to have been included inappropriately, and the vast majority of the births included in the perinatal death outcomes are from studies that did not provide statistics compatible with Wax and colleagues' definition of perinatal death.

Finally, it is surprising that the 2009 study by Janssen and colleagues[19] was not included in the nonanomalous perinatal death outcome, because it does appear to provide adequate information to be included in this row. Similarly, the study by Lindgren and colleagues[18] appears to provide adequate information to be included in both the all perinatal death and nonanomalous perinatal death outcomes. Koehler, Solomon, and Murphy[13] also describe perinatal mortality, although difficulties are associated with their definition of perinatal mortality.

In reviewing the 12 cited studies, we have found a variety of definitions of perinatal mortality and frequent omission of complete descriptions of which deaths are and are not reported. This issue would appear to make combining studies of perinatal mortality in any meaningful way to be very challenging. It is very surprising that Wax and associates did not mention this limitation at all.

With respect to other reported outcomes, we have not completed an exhaustive search for improperly included and excluded studies but have found some additional exclusions, for example, the study by Hutton, Reitsma, and Kaufman[12] and Janssen and colleagues' 2002 study[15] were not included in the perineal laceration outcome and the latter was also not included in the ≥ third-degree laceration outcome.

For a study in which the main results arise from distinctions between precisely defined categories, such as perinatal vs neonatal death and nonanomalous vs all newborns, the issue of improper inclusion/exclusion is of utmost importance, and we have described many specific examples where studies were included or excluded incorrectly.

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