BMJ  2004;329:359-360 (14 August), doi:10.1136/bmj.329.7462.359

Editorial

Vaginal delivery after caesarean section

Determining thresholds for risks requires more than uterine rupture rates

Once considered unthinkable, vaginal delivery after a previous caesarean section remains a safe option for many women. One of the greatest concerns for patients, providers, hospitals, and policy makers with regard to vaginal delivery after prior caesarean is the potential for devastating consequences such as perinatal death from uterine rupture. Although the risk factors associated with uterine rupture have been investigated often, few studies have attempted to measure mortality and morbidity directly related to uterine rupture, and none has examined whether outcomes related to uterine rupture are related to the number of births per year in the hospital. This editorial discusses the current evidence regarding risk factors for catastrophic uterine rupture and possible preventive measures, and considers the importance of framing risk in policy, and discussions between provider and patient.

Uterine rupture remains a rare event

In this issue Smith et al present population based data from the Scottish birth registry, confirming that uterine rupture is a rare event, occurring in 3.5 per 1000 trials of labour.¹ A recent systematic review of studies found a rate of 2.7/1000 trials of labour.² The study by Smith et al also confirmed the finding of previous studies, that by itself induction of labour does not increase the risk of rupture.¹

Association is not causation

The Scottish study contributes to the mounting evidence that vaginal delivery is more likely and uterine rupture less likely for women with prior vaginal delivery than for women without (1/514 v 1/210).¹ As in a previous study from Washington state, this study found that use of prostaglandin was associated with uterine rupture.³ However, association is not causation. Differences between patients induced with prostaglandins and differences in monitoring vigilance may act as confounders. For example, an unfavourable cervix is associated with a prolonged and difficult labour, increasing exposure time and perhaps the length and strength of contractions. Unlike oxytocin, which requires frequent visits from nurses (every 15-30 minutes) to adjust the dose, prostaglandins, with their four to six hour dosing, may be associated with decreased vigilance and delayed intervention.

Prevention strategies

The study by Smith et al is the first to examine the relation between hospitals with higher numbers and lower mortality related to uterine rupture. This finding is thought possibly to reflect in-house availability of providers of anaesthesia and obstetric care and thus rapid response time, and it provides indirect support for the American College of Obstetricians and Gynecologists' position that response time is critical.⁴ Until now, only two case-control studies have examined the association between response time and morbidity related to uterine rupture. The first and largest found that no cases of death or asphyxia occurred if the time between fetal bradycardia and delivery was under 18 minutes.⁵ A more recent and thorough, though smaller, case-control study that examined reasons for delay, such as delayed decision making, did not concur.⁶ These studies show that in patients at high or uncertain risk, examination of safety should be carried out in larger hospitals with the ability to respond rapidly. Although this initially leaves small hospitals with limited options, ultimately it may give them more options as we refine our understanding of situations that truly entail a high risk rather than abandoning the procedure entirely.

International collaboration and improved outcome measures

Women want the best possible evidence to understand their risk and make educated choices. Unfortunately, despite numerous studies their observational nature and rarity of the condition present severe limitations. In cases of rare events with multifactorial contributors, large registries and trials are necessary to tease out the true contributors to risk and preventive interventions. With a focus on integrity of outcomes and accuracy of reporting, modern technology can enable us to conduct high quality, large scale, national and international research to identify those few situations where vaginal delivery after prior caesarean is simply too risky.

Framing risk under conditions of uncertainty

In their Nobel prize winning work, Tversky and Kahneman discovered that framing of outcomes, choices, and contingencies influences decision making.^{7 8} The reference points and language we choose as providers and policy making organisations influence public perceptions, policy formulation, and the climate for practice and research. Whether discussions highlight benefits or risks and whether the portrayal is relative or absolute can affect perceptions.

The public often behaves as if the risk threshold is set at perfection and no risk is acceptable. Yet in some circumstances they are willing to accept similarly rare yet catastrophic adverse events for elective procedures even if there are acceptable alternatives. For example, elective tubal sterilisation has a chance of failure (resulting in, for example, pregnancy) in the order of one in 200. The result could be an ectopic pregnancy, a leading cause of maternal death in pregnancy. Despite the gravity of this potential adverse event, the benefits of contraception are thought by many to outweigh the rare chance of failure and maternal death. Pregnancy and childbirth are inherently risky, with perinatal death rates ranging from 2.3 per 1000 to 192.5 per 1000 internationally, and reaching 4.8/1000 in Canada, 5.2/1000 in the United Kingdom, and 6.6/1000 in the United States.⁹ Modern technology and superior medical care cannot remove all risk completely. As international attention focuses on harms, rare threats to global health, and reduction of risk, we need to be mindful of our consistency and thoughtfulness in evaluating risks as the language we choose affects public perception and our clinical and research environment. Thus to decide on thresholds for risk for vaginal delivery and repeat caesarean section we need to look at rates for harms such as uterine rupture and benefits, and also ensure consistency with other issues when we interpret the thresholds.

Oregon Health and Science University Department of Obstetrics and Gynecology, UHN-50, 3181 SW Sam Jackson Park Road, Portland, OR 97239-3098, USA (guisej{at}ohsu.edu)

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Papers p 375

Competing interests: None declared.

References

1. Smith GC, Pell JP, Pasupathy D, Dobbie R. Factors predisposing to perinatal death related to uterine rupture during attempted vaginal birth after caesarean section: retrospective cohort study. BMJ 2004;329: 375-7.[Abstract/Free Full Text]
2. Guise JM, McDonagh MS, Osterweil P, Nygren P, Chan BK, Helfand M. Systematic review of the incidence and consequences of uterine rupture in women with previous caesarean section. BMJ 2004;329: 19-25.[Abstract/Free Full Text]
3. Lydon-Rochelle MT, Holt VL, Martin DP. Delivery method and self-reported postpartum general health status among primiparous women. Paediatr Perinat Epidemiol 2001;15: 232-40.[CrossRef][ISI][Medline]
4. ACOG Practice Bulletin #54: vaginal birth after previous cesarean. Obstet Gynecol 2004;104: 203-12.[Free Full Text]
5. Leung AS, Leung EK, Paul RH. Uterine rupture after previous cesarean delivery: maternal and fetal consequences. Am J Obstet Gynecol 1993;169: 945-50.[ISI][Medline]
6. Bujold E, Gauthier RJ. Neonatal morbidity associated with uterine rupture: What are the risk factors? Am J Obstet Gynecol 2002;186: 311-4.[CrossRef][ISI][Medline]
7. Tversky A, Kahneman D. The framing of decisions and the psychology of choice. Science 1981;211: 453-8.[Abstract/Free Full Text]
8. Kahneman D, Tversky A. Prospect theory: an analysis of decision under risk. Econometrica 1979;47: 263-91.[CrossRef][ISI]
9. Central Intelligence Agency. The world factbook. Washington: CIA, 2004; Rank order—infant mortality rate. www.odci.gov/cia/publications/factbook/fields/2091.html (accessed 5 Aug 2004).

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