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

More Methodological and Reporting Errors

Invalid Statistical Test

Wax and colleagues begin their discussion by remarking on the robustness of the neonatal death statistics, supported by the homogeneity of the observation across studies.[1] Homogeneity is said in the methods section to have been assessed with the Breslow-Day test. This test is not, however, valid for any of the perinatal or neonatal death outcomes. The user guide for SAS® 9.2 (SAS, Cary, NC), which the investigators claim to have used, states: "For the Breslow-Day test to be valid, the sample size should be relatively large in each stratum, and at least 80% of the expected cell counts should be greater than 5."[23] These criteria are not met for any of the mortality outcomes. The ORs for the individual, included studies range in some cases from 0 to infinity. It is not at all obvious that the studies are statistically homogeneous.

Association and Causation Conflated

Wax and colleagues claim that "less medical intervention during planned home birth is associated with a tripling of the neonatal mortality rate."[1] This is the sole conclusion offered in the abstract. Although it may be unintentional, the discussion in the paper implies that the reasons for an increase in neonatal mortality are derived from the studies that were included in the meta-analysis. However, the discussion of causes of neonatal mortality focuses on findings from studies that were not included in the meta-analysis, including studies that mix high-risk with low-risk cases.[24,25,26,27] Of the studies that are included in the meta-analysis, none associates rates of intervention with rates of neonatal mortality.

Any discussion of causation for elevated neonatal death rates for planned home births compared with planned hospital births is particularly specious in light of the paradoxical nature of the results it attempts to explain -- the results reproduced in Table 1 above. Furthermore, as part of their discussion of causation, Wax and colleagues claim that planned home births were characterized by a greater proportion of deaths attributed to respiratory distress and failed resuscitation. No data are provided in support of this claim, but 4[11,13,14,18] of the 12 primary articles are cited. However, not a single death in the home birth group in the study by Woodcock and associates[11] was attributed to respiratory distress or failed resuscitation. In the study by Lindgren and associates,[18] 1 of 2 home birth fatalities is attributed to asphyxia, whereas 4 of 7 in the hospital group list asphyxia in the cause of death. Koehler, Solomon, and Murphy[13] reported 1 death of an infant who had no onset of spontaneous respiration; in this study, the hospital birth comparison group consisted of only 67 births with no deaths reported. It is very difficult to see how these 3 studies could be interpreted to support the claim made by Wax and colleagues.

The entire discussion of causation is further undermined by the numerous numerical errors, and issues of inclusion and exclusion described above.

Errors in the Abstract

The abstract states that the results revealed less frequent assisted newborn ventilation in planned home births. However, this is inconsistent with the body of the article, where the result is not statistically significant but trends towards increased frequency. The spuriously statistically significant result for perineal laceration produced by the faulty spreadsheet results in another outcome that is incorrectly reported in the abstract. Significant additional errors in the abstract are associated with the mistaken inclusion/exclusion issues already described.

Shifting Numbers

Following a post-publication investigation of the study initiated by the American Journal of Obstetrics and Gynecology,[28] Wax published a supplement containing forest plots and summary tables.[8] The summary ORs and CIs for 3 of the reported outcomes (nonanomalous neonatal death, postdates, and prematurity) differ from their values in the originally published paper. Although none of these changes alters the direction of the reported result or its statistical significance, it is very surprising that Wax made no mention of these changes. None of the 3 updated outcomes yet provides correct values; for postdates and prematurity the faulty calculator was used, whereas the nonanomalous neonatal death outcome suffers from data extraction and mistaken inclusion errors.

Differences Among Studies

The group of studies included in this meta-analysis presents a number of additional statistical problems. Most, but not all, of the studies restricted inclusion to low-risk births. Most (by population), but not all, of the studies restricted home births to those attended by certified or licensed midwives. Most (by population), but not all, of the studies included only midwives operating in jurisdictions where midwives offering home birth services are well integrated into the greater healthcare system. All but a single study restricted home births to those that were planned.

Wax and coworkers make little mention of any of these complications, and it would seem that any conclusions made on the basis of combined results from such a disparate set of conditions would not be relevant to any parent planning a birth. Given these complexities, decisions would be better made on the basis of the subset of studies that are relevant to the conditions at hand.

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