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The impact of hospital obstetric volume on maternal outcomes in term, non-low-birthweight pregnancies

Snowden JM et al. (2014)

American Journal of Obstetrics and Gynecology, online 28 September 2014

Editor’s comment: Prof. Jim Thornton: Relation between post-partum haemorrhage and small rural hospitals in California

In a large retrospective study from California, after adjustment for case-mix, there were no statistically significant associations between delivery complications and hospital size, with one exception. Post-partum haemorrhage was significantly more common (adjusted odds ratio 3.06 95% confidence interval 1.51-6.23) in the smallest category of rural hospital (50-599 births per annum).



The impact of hospital obstetric volume specifically on maternal outcomes remains under-studied. We examined the impact of hospital obstetric volume on maternal outcomes in low-risk women delivering non-low-birthweight infants at term.

Study Design

We conducted a retrospective cohort study of term, singleton, non-low-birthweight live births between 2007 - 2008 in California. Deliveries were categorized by hospital obstetric volume categories, separately for non-rural hospitals (Category 1: 50 – 1,199 deliveries per year; Category 2: 1,200 – 2,399; Category 3: 2,400 – 3,599, and Category 4: ≥3,600) and rural hospitals (Category R1: 50 – 599 births per year; Category R2: 600 – 1,699; Category R3: ≥1,700). Maternal outcomes were compared using the chi-square test and multivariable logistic regression.


There were 736,643 births in 267 hospitals that met study criteria. After adjusting for confounders, there were higher rates of postpartum hemorrhage in the lowest-volume rural hospitals (Category R1 aOR 3.06; 95% CI 1.51 – 6.23). Rates of chorioamnionitis, endometritis, severe perineal lacerations, and wound infection did not differ between volume categories. Longer lengths of stay were observed after maternal complications (e.g., chorioamnionitis) in the lowest-volume hospitals (16.9% prolonged length of stay in Category 1 hospitals versus 10.5% in Category 4 hospitals; aOR, 1.91; 95% CI, 1.01 - 3.61 ).


After confounder adjustment, few maternal outcomes differed by hospital obstetric volume. However, elevated odds of postpartum hemorrhage in low-volume rural hospitals raises the possibility that maternal outcomes may differ by hospital volume and geography. Further research is needed on maternal outcomes in hospitals of different obstetric volumes.


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Commentaries by Editor Prof. Jim Thornton