by Henci Goer

Commentary on: Lydon-Rochelle, M., et al. Risk of uterine rupture during labor among women with a prior cesarean delivery. N Engl J Med 2001;345(1):3-8. [Abstract]

Study design and results: evaluation of 20,095 Washington State women having a second child after having the first by cesarean section.

• Chances of the scar giving way (uterine rupture):
  • elective cesarean section: 1.6 per 1,000
  • spontaneous labor onset: 5.2 per 1,000
  • induced labor, no prostaglandin: 7.7 per 1,000
  • induced labor with prostaglandin: 24.5 per 1,000
• Chances of hysterectomy or infant death: (Note: The investigators did not report these outcomes. I calculated them from study data.)
  • elective cesarean section: hysterectomy 1 per 10,000; infant death 1 per 10,000
  • spontaneous labor onset: hysterectomy 2 per 10,000; infant death 3 per 10,000
  • induced labor, no prostaglandin: hysterectomy 3 per 10,000; infant death 4 per 10,000
  • induced labor with prostaglandin: hysterectomy 11 per 10,000, infant death 13 per 10,000

Problems include but are not limited to the following:

• The study showed only that using prostaglandins to induce labor was risky, not VBAC per se: The scar rupture rate with spontaneous labor onset is similar to that found in other studies of VBAC and a mere 4 additional cases in every 1000 compared with planned c-section. Even when oxytocin is used to induce labor, the rate is still less than 1 in 100 VBACs and not much greater than that seen with spontaneous labor. By contrast, the use of prostaglandin to induce labor drives the scar rupture rate up to more than 2 per 100, although even here, 97.5% of women who labor will have no problem with the scar.
  
  
• The issue isn't the rate of uterine rupture during VBAC, but whether it results in irremediable harm to mother or baby: The accompanying editorial claimed that this study had unequivocally proven that elective repeat cesarean section was safer for babies.(1) But hysterectomy and infant death rates differ by only a miniscule amount between planned VBAC with spontaneous labor onset and planned cesarean (1 excess hysterectomy per 10,000 and 2 infant deaths per 10,000). Differences aren't much greater with labors induced with oxytocin (2 excess hysterectomies per 10,000 and 3 infant deaths per 10,000). For comparison's sake, amniocentesis results in an excess loss of 60 pregnancies per 10,000, yet obstetricians do not question the safety of amniocentesis.(2)
  
  
• The accuracy of the data is highly questionable: Lydon-Rochelle and colleagues used birth certificate data and medical diagnosis codes as data sources, but studies show that these sources are riddled with errors and misclassifications.(3) In proof of this, 267 women in the VBAC group were coded as having breech babies and 44 as having placenta previa. Without doubt these births would have been planned cesareans.
  
  
• You can't determine whether elective cesarean section is better than VBAC just by looking at uterine rupture rates: A host of adverse outcomes associated with surgical delivery occur more often with c-section.(4,5) These include increased risk of maternal death, blood clots and stroke, surgical injury, infection, readmission to hospital, and neonatal respiratory problems. In fact, the study obscures the relationship between surgical complications and repeat cesarean by reporting rates of severe posthemorrhagic anemia, major infection, bladder injury, paralytic ileus (paralyzed bowel), and “other surgical complications” according to “no uterine rupture” and “uterine rupture” groups rather than planned VBAC versus planned cesarean groups. This dilutes the “no rupture” group with the many women who had vaginal births, giving a misimpression of how often these complications occur in connection with planned cesarean surgery.
  
  
• You can't determine whether elective repeat cesarean is the better option without considering the long-term consequences for mother and baby (4): For the mother, surgery exposes her to increased likelihood of experiencing chronic pelvic pain, and bowel obstruction due to adhesions. The probabilities of these will almost certainly rise with additional surgeries. In addition, increasing amounts of pelvic scar tissue makes future surgeries more technically difficult for the surgeon and operative injury more likely. Babies developing in a cesarean-scarred uterus are more likely to be ectopic pregnancies (the embryo implants outside of the uterus), to die in late pregnancy, or to be born preterm, low-birth-weight, or have a congenital anomaly. We do not know if having multiple cesareans increases the chances of perinatal mortality and morbidity, but it stands to reason that it would if uterine scarring is the root cause. Studies also show that accumulating cesarean scars increases the likelihood of placenta previa (the placenta overlays the cervix) and of having placenta accreta (the placenta grows into or through the uterine muscle) in conjunction with placenta previa. Placenta accreta is particularly deadly for babies and mothers because it almost invariably causes massive hemorrhage.(6) The incidence of placenta accreta has increased 10-fold—from 1 in 25,000 deliveries to 1 in 2500 deliveries— over the last 50 years, a rise attributed to the rise in cesarean surgery.(7)

Comment: This study exemplifies a disturbing pattern that has emerged recently: an extremely flawed study appears in a respected journal; it is accompanied by an editorial that makes exaggerated claims far beyond the scope of the study's own dubious results; the study and especially the editorial are widely publicized; this triggers a wide-spread, almost overnight change in policy; months later, commentaries and letters to the editor appear pointing out the flaws, but to no avail.

Bibliography:

1. Greene M. Vaginal delivery after cesarean section—is the risk acceptable? N Engl J Med 2001;345:54-5.
2. Seeds JW. Diagnostic mid trimester amniocentesis: how safe? Am J Obstet Gynecol 2004;191:608-16.
3. Guise JM, et al. Systematic review of the incidence and consequences of uterine rupture in women with previous caesarean section. BMJ 2004;329:159-65.
4. Childbirth Connection. Should I choose VBAC or repeat c-section? Available online at http://www.childbirthconnection.org/article.asp?ClickedLink=293&ck=10212&area=27
5. Childbirth Connection. What should I know about cesarean section? Available online at http://www.childbirthconnection.org/article.asp?ClickedLink=274&ck=10168&area=27
6. O'Brien JM, Barton JR, & Donaldson ES. The management of placenta percreta: conservative
   and operative strategies. Am J Obstet Gynecol 1996;175(6):1632-8.
7. ACOG. Placenta accreta. Committee Opinion No. 266, Jan 2002.