Rates for obstetric intervention among private and public patients in Australia: population based descriptive study

British Medical Journal, July 15, 2000 by Christine L Roberts, Sally Tracy, Brian Peat

We examined the rates of obstetric interventions among women at low risk for three patient and hospital groups: private patients giving birth in private hospitals, private patients giving birth in public hospitals, and public patients giving birth in public hospitals. We examined a prespecified cascade effect of obstetric interventions by grouping them in chronological sequence--those interventions that occur during labour but before birth (epidural and induction or augmentation of labour) followed by those that occur at the time of birth (episiotomy and type of delivery). Induction and augmentation are grouped together for simplicity of presentation as the outcomes were similar after these interventions and because the intervention is similar for women and only differs in whether it occurs before or after labour has begun.

Analysis

Associations between patient and hospital group and maternal, infant, and clinical factors were examined by contingency table analyses. Because of the large number of births and statistical comparisons made, the significance level for all statistical testing was set at P [is less than] 0.01. As the age distribution differed among private and public women at low risk, we calculated age adjusted intervention rates by direct standardisation, with the pooled low risk population as the standard. The probabilities of interventions are presented as age adjusted rates per 100 women for each of four subgroups of labour management before birth. The absolute probability of each end point can be obtained by multiplying the end point probability for the subgroup by the probability for the entire subgroup. Analyses were conducted with SAS through the New South Wales health department's Health Outcomes Information and Statistical Toolkit (HOIST) data warehouse system.

Results

Of 171 157 livebirths, we excluded 95 without a public or private classification recorded and 356 home births. Of the remaining 170 706 women, 31.6% (53 947 women) were private patients and 68.4% (116 759) were public patients. Private patients were more likely to be older, have lower parity, be without medical or obstetric complications, and have non-cephalic presenting infants and twin pregnancies, and their infants were likely to be heavier (table 1). Although these differences were highly significant (P [is less than] 0.001), the absolute magnitudes of many were small (table 1). Just under half of the women had pregnancies that were classified as low risk. Over half of private patients gave birth in private hospitals and this was true for both primiparas (58%) and multiparas (55%) at low risk. Among low risk primiparas, private patients in private hospitals were significantly more likely to have obstetric interventions compared with public patients and were less likely to have spontaneous onset of labour or a non-instrumental vaginal birth (table 2). For all interventions, the rates for private patients in public hospitals fell between those of private patients in private hospitals and public patients.