Adverse outcomes of labour in public and private hospitals in Australia

To the Editor: Robson and colleagues found higher crude odds of perinatal death in public hospitals — an unsurprising finding, given the maternal demographics in the public system.1 However, after taking into account known risk factors for poor perinatal outcome by “adjusting for the potentially confounding variables available in the NPDC [National Perinatal Data Collection]”, the authors found that the odds ratio actually went up — implying that the pregnancies of mothers in the private system are higher risk. This is implausible.

There are a number of problems with the analysis. The possibility that potentially important maternal information was not included has been acknowledged.1,2 Of greater concern is the omission of a history of low birthweight from the regression model. Since intrauterine growth retardation is a very strong risk factor for perinatal death,3 and since the rate of low birthweight in the public hospitals was double that in the private hospitals, this omission is puzzling.

Furthermore, while the authors’ stated aim was to assess the effect of the private model of obstetrician-led interventional care on perinatal outcomes, they included the method of birth and hospital type as independent explanatory variables. Since the interventional nature of obstetric care is, as acknowledged by the authors, a key component of the model of care provided in a private hospital, adjusting for this variable will lessen the usefulness of the study in assessing the impact of private hospital care on perinatal outcomes. Put another way, in deciding what is best for her baby, a mother who is considering giving birth in the private system cannot cherry-pick only the non-interventional side of the obstetrician-led model of care — she must adopt the entire package.

Including method of birth as a separate explanatory variable artificially inflates the apparent “riskiness” of the pregnancies of mothers presenting to private hospitals to give birth. These mothers had a 75% increased incidence of caesarean section; however, most of these procedures would be elective rather than emergency. Since this distinction was not made, the women in private hospitals appear high risk despite having had a caesarean section for a low-risk pregnancy. This will have the effect of making perinatal outcomes in private hospitals appear more favourable than they actually are.

As currently analysed, the data are of little value to prospective mums and dads in making the first, and one of the most emotive, of the many decisions they need to make as parents.