Cesarean section and uterine rupture

Two recent studies--one still in press--that I find quite fascinating relating to uterine rupture. I have the full text of the first one, and hope to access the second one* as soon as it is officially published. As always, email me if you'd like to take a look at the full text.

A few comments/questions/observations:

• I hope that the evidence from the first study won't be used to risk out women who never went into labor before their cesarean section. Instead, I hope it will simply be used to give extra confidence and reassurance to women who did experience labor before they had a cesarean.
• In the second study, note the correlation between oxytocics (i.e., Pitocin) and uterine rupture in both scarred and unscarred uteri. 21 of the 41 uterine true ruptures occurred in connection with oxytocics--9 among women with previous cesarean sections and 12 among women with unscarred uteri. This, of course, doesn't mean that using Pitocin = uterine rupture, but certainly it suggests the need for prudence and caution when administering Pitocin during labor--not just among women having a VBAC, but also among women with no previous cesarean section.
  

1) Laboring before a primary C/S reduces the risk of uterine rupture in a subsequent intended VBAC
C.S. Algert et al. "Labor before a primary cesarean delivery: reduced risk of uterine rupture in a subsequent trial of labor for vaginal birth after cesarean." Obstet Gynecol. 2008 Nov;112(5):1061-6.

OBJECTIVE: To estimate the effect of the onset of labor before a primary cesarean delivery on the risk of uterine rupture if vaginal birth after cesarean (VBAC) is attempted in the next pregnancy.
METHODS: Longitudinally linked birth records were used to follow women from a primary cesarean delivery to a trial of labor at term for their next birth. The effects of characteristics of both the trial of labor and primary cesarean deliveries on the risk of uterine rupture were examined.
RESULTS: Of 10,160 women who had a trial of labor, 39 (0.38%) had a uterine rupture. Women who were induced or augmented for their trial of labor had a greater relative risk (RR) of uterine rupture (crude RR 4.24, 95% confidence interval [CI] 2.23-8.07). Women whose primary cesarean delivery was planned or followed induction of labor also had an increased risk of uterine rupture (crude RR 2.61, 95% CI 1.24-5.49), and this risk remained after adjustment for other factors. Women with a history of either spontaneous labor or vaginal birth had one uterine rupture for every 460 deliveries; women without this history who required induction or augmentation to proceed with a VBAC attempt had one uterine rupture for every 95 deliveries.
CONCLUSION: Labor before the primary cesarean delivery can decrease the risk of uterine rupture in a subsequent trial of labor. A history of primary cesarean delivery preceded by spontaneous labor is favorable for VBAC.
LEVEL OF EVIDENCE: II.

2) Half of all true uterine ruptures are not associated with prior cesarean section
Porreco RP, Clark SL, Belfort MA, Dildy GA, Meyers JA. The changing specter of uterine rupture. Am J Obstet Gynecol. 2009 Jan 9. [Epub ahead of print] Presbyterian/St. Luke's Medical Center, Denver, CO.

OBJECTIVE: The objective of the study was to review all patient records discharged with codes for uterine rupture in 2006 in Hospital Corporation of America hospitals. STUDY DESIGN: All patient charts were distributed to a committee of perinatologists and general obstetricians. Case report forms were analyzed for variables of interest to determine validity of coding and quality of care.
RESULTS: Of 69 cases identified, only 41 were true ruptures. Twenty patients had previous cesareans, and in 9 of these patients, concurrent use of oxytocics was documented. Among the 21 patients without previous cesareans, 7 had previous uterine surgery, and oxytocics were documented in 12 of the remaining 14 patients. Standard of care violations were identified in 10 of 41 true rupture cases.
CONCLUSION: Epidemiological data on uterine rupture based on hospital discharge codes without concurrent chart review may be invalid. Patients with previous cesareans represent only half of true uterine ruptures in contemporary practice.

* thanks to Jill for this one!