I: Critical Appraisal of Studies in Section B (Studies with Errors in Design, Analysis or Reporting)
Each paper is linked to either its original abstract on PubMed or the full-text article if available; click on the title to be taken to the abstract/ article.
A) Michal, C. A., Janssen, P. A., Vedam, S., Hutton, E. K., de Jonge, A. (2011). Planned home vs hospital birth: A meta-analysis gone wrong. Medscape Ob/Gyn & Women’s Health. (full text)
For a detailed analysis of the 2012 Wax meta-analysis see Section B.I.A. Authors include principal investigators for 3 of the original studies included in the meta-analysis. Each of the significant numerical, statistical and logical errors, errors in definitions, errors in inclusion/exclusion of data for analysis, and mistaken conflation of association with causation, are delineated. Methodological problems and a faulty computational tool are described.
B) Gyte, G., Newburn, M., & Macfarlane, A. (2010). Critique of a metaanalysis by Wax and colleagues which has claimed that there is a three-times greater risk of neonatal death among babies without congenital anomalies planned to be born at home. NCT. (full text)
Detailed review of Wax’s meta-analysis outlining a range of data reporting errors and methodological weaknesses, which include: insufficient details about choice of included and excluded studies, lack of clarity or consistency about the definition of neonatal mortality, including whether stillbirth data were included. Wax misclassified singleton newborns with a gestational age of 34 wks who were born after transfer from home as ‘planned’ home birth if birth certificate indicated delivery was initially attempted at home. Gyte argues that the authors’ conclusion that “less medication intervention during planned home birth is associated with a tripling of neonatal mortality rate” is unsupported by the poor quality of their data and that the article should not have been accepted by AJOG.
Commentary on Wax JR et al. Maternal and newborn outcomes in a planned home birth vs. planned hospital birth. Keirse highlights the weakness and results of Wax et al.’s meta-analysis of home birth. Keirse examines which studies Wax included and excluded from his meta-analysis in order to conclude that home birth is related to a 2.6 increase of maternal mortality and a tripling of neonatal mortality. Keirse also cites either statistical errors or reporting errors of data present in the study that contribute to his results. Wax’s meta-analysis refers only to planned home birth but includes statistics from U.S. birth certificates that do not differentiate between planned and unplanned home birth, and this inclusion significantly contributes to the higher rate of neonatal mortality. Although useful when randomized control trials are unavailable, meta-analyses need to consider the impact culture, geography, and health care systems have on data when consolidating smaller studies.
D) de Jonge, A., Mol, B. W., Van der Goes, B. Y., Nijhuis, J. G., Van der Post, J. A., & Buitendijk, S. E. (2010). Too early to question effectiveness of Dutch maternity care system. Commentary on: Perinatal mortality and severe morbidity in low- and high-risk term pregnant women in the Netherlands: A prospective study. BMJ 341:c7020.
Detailed review of prospective cohort study by Evers et al. that identifies several weaknesses in the study’s methodology which include: a retrospective definition of “population of risk” despite claims that the study is a prospective cohort study; all intrapartum deaths were included but not all births; for midwives whose practices cross boundaries, deaths outside catchments were included in the study but not births, which hence artificially inflated the mortality rate. The neonatal mortality rates in this region are twice as high as the rates of previous national studies, which requires further investigation. In the Netherlands primary maternity care often is equated with midwifery care. Evers et al. suggest that home birth is the cause of increased perinatal morbidity, but there is no data presented that links site of birth or planning status to the reported outcomes. Data of a large birth registry database were used and adjustment for confounders, including appropriate referrals from primary to secondary care before the onset of labour, was not possible. Given so many discrepancies from national studies, the authors find that Evers et al.’s conclusion that “the obstetric care system in the Netherlands possibly contributes to the high perinatality mortality rate” is not supportable.
E) Vedam, S. (2003). Home versus hospital birth: questioning the quality of the evidence on safety. Birth, 30(1):57-63.
Detailed review of Pang’s study, including well acknowledged errors in methodology and definitions. Outlines flaws associated with using birth certificate data to study outcomes of planned home births and includes an algorithm for evaluating quality of studies on home birth safety. Studies must adhere to following study design criteria in order to avoid errors and bias: 1) differentiate between planned and unplanned home births, 2) accurately discriminate between provider types, 3) use consistent inclusion criteria across groups, 4) adjust for home birth selection criteria, 5) control for transfer criteria and 6) select consistent outcome measures. Compares the methodology used by Pang with the methodology of other commonly cited home birth studies, with examples of reliable and unreliable designs.