Practice Variation: Induction Rates at University vs. Community Hospitals

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Guest post by Jessica Turon

 

The Basics

Many studies on the rising cesarean and induction rates focus on maternal risk factors, but it’s also clear that rates vary a lot from hospital to hospital. Does hospital variation reflect differing patient populations? Or is the variation due to different hospital characteristics, patients aside? Jill asked me to review this article, which looks at whether hospital type (university versus community) is associated with the rates of term labor inductions and cesareans if certain maternal characteristics are held constant.

 

The Boring Part

The paper is a retrospective cohort study based on Ohio birth certificate data in 2006-2007. (Did you know birth certificates had all that data on them? The one in your files at home sure doesn’t!) The investigators included only births from 20 weeks through 42 weeks, in known hospitals, and excluded fetal deaths and births with major congenital anomalies, for n=283,370.* The analyses of induction and cesarean rates further limited the study population to births from 37-42 weeks, for n=244,464.

 

The Results

As expected, they found that university hospitals had a somewhat higher-risk population in terms of maternal morbidities, and adjusted for these in the analyses. The comparison of labor induction rates at university versus community hospitals was notable:

  • at 37 weeks, the odds were 1.7:1, or about a 50% higher risk at community hospitals**
  • at 38 weeks the odds were 1.8:1, or about a 54% higher risk
  • and at 39 to ≤42 weeks, the odds were 2.0:1, or about a 60% higher risk

Unlike induction, cesarean rates showed no significant differences between community and university hospitals.

 

What’s it Mean?

Overall, this study is of good enough quality to show that in Ohio in 2006-7, community hospitals were much likelier to induce women at term than university hospitals.

More broadly, this study is a good piece of evidence about how hospital characteristics – not just maternal characteristics – can influence hospital-level rates of various obstetric practices. This is a topic that definitely needs more study!

Does this study provide information on what kind of hospital to deliver at, if you’re planning a hospital birth? The answer is “not really” – these data are more useful for policy-makers, hospital administrators, and so forth. The association found here was significant, but not huge, and the study looked at only one hospital characteristic.*** It’s probably more helpful to ask questions about the individual hospitals you’re considering, like whether they have midwives on staff, or their specific induction and cesarean rates.

You might be wondering why cesarean rates didn’t go up along with inductions, given what’s known about the association between them. The authors wondered too, and gave some background on how that association has been studied. This study can’t comment on the relationship, though, because the relevant data here is cross-sectional. In other words, we don’t know if the women having the inductions were the ones having the cesareans, so we can’t see the relationship between the two in the individual woman. Although we’d expect higher cesarean rates at the community hospitals to accompany their higher induction rates, this paper can’t explain why we don’t get that result.

 

Data Wonk Notes

*Oddly, the study looked at differences in maternal morbidity by hospital type among women giving birth between 21 and 42 weeks (n=283,370) and then used that data in the logistic regression to adjust for the smaller, presumably healthier population giving birth only at term (n=244,464). If this were corrected, it would likely have the effect of making the hospital types look more similar, which in turn would mean less adjustment, meaning the odds ratio would be lower.

**The paper makes a common mistake in interpreting the odds ratio that I have attempted to correct. They write “During gestational week 37, women who delivered in community hospitals were 70% more likely to undergo induction than those in university hospitals (27% vs 19%; aOR, 1.7; 95% CI, 1.5–1.8)” (page 346.e3). Unfortunately, this is the incorrect interpretation of an odds ratio (versus a risk ratio); more information here. I used this tool to correct it for the “% more likely” information I gave above. [They follow this up with “80% of the women were more likely to undergo induction in week 38 of gestation  (31% vs 21%; aOR, 1.8; 95% CI, 1.7–2.0)” which I am assuming is an editing error as it makes no sense otherwise.]

***They also looked at teaching versus non-teaching hospitals as an exposure and found similar but weaker results. There wasn’t a chart for this data or any explanation of confounders or adjustment.

 

And finally

If “Epidemiology Trail” were a game, I would probably be dead of dysentery. Did I get something wrong? Please tell me in the comments!

 

Snyder CC, Wolfe KB, Loftin RW, et al. The influence of hospital type on induction of labor and mode of delivery. Am J Obstet Gynecol 2011;205:346.e1-4.