It is important to note that the information shared in Guise (2010), the 400 page Evidence Report on which the 2010 NIH VBAC Conference was based, collected the best data we have available on trial of labor after cesarean. That said, they reported, “Overall, the strength of evidence on perinatal mortality was low to moderate” due to the wide range of perinatal mortality rates reported by the studies included in the report. Bottom line: We still don’t have an accurate idea of how deadly uterine rupture is to babies. This is a topic on which Guise recommended future researchers focus. I highly recommend that anyone interested in TOLAC (trial of labor after cesarean), especially those who blog or share information on social networking sites, review this very important document as it is a fascinating analysis of the best research we have to date on TOLAC.
How many times have you heard, “Only 6% of uterine ruptures are catastrophic” or “Uterine rupture not only happens less that one percent of the time, but the vast majority of ruptures are non-catastrophic?” But what does that mean? Does that mean only 6% of uterine ruptures are “complete” ruptures? Result in maternal death? Infant death? Serious injury to mom or baby? This article will explain to you the difference between uterine rupture and uterine dehiscence as well as explain the source and meaning of the 6% statistic.
Distinguishing between uterine rupture and uterine dehiscence
First, it’s important to understand what a uterine rupture is and how that differs from a uterine dehiscence. Uterine rupture, also called true, complete, or even (to further add to the confusion) catastrophic rupture, is a opening through all the layers of the uterus. Per a Medscape article on Uterine Rupture in Pregnancy:
Uterine rupture is defined as a full-thickness separation of the uterine wall and the overlying serosa. Uterine rupture is associated with (1) clinically significant uterine bleeding; (2) fetal distress; (3) expulsion or protrusion of the fetus, placenta, or both into the abdominal cavity; and (4) the need for prompt cesarean delivery and uterine repair or hysterectomy.
Whereas a uterine dehiscence, also called a incomplete rupture or a uterine window, is not a full-thickness separation. It’s often asymptomatic, does not pose any risk to mom or baby, and does not require repair. Again, I refer to Medscape:
Uterine scar dehiscence is a more common event that seldom results in major maternal or fetal complications. By definition, uterine scar dehiscence constitutes separation of a preexisting scar that does not disrupt the overlying visceral peritoneum (uterine serosa) and that does not significantly bleed from its edges. In addition, the fetus, placenta, and umbilical cord must be contained within the uterine cavity, without a need for cesarean delivery due to fetal distress.
When reading medical studies, look for how they define uterine rupture in the “Methods” section. While some medical studies combine the statistics for rupture and dehiscence, ultimately reporting an inflated rate of rupture, other studies distinguish between the two events.
So, what does the 6% statistic mean and where did it come from?
The statistic “Only 6% of uterine ruptures are catastrophic” is from the Evidence Report (Guise 2010) which was the basis of the 2010 NIH VBAC Conference and it refers to the rate of infant death due to uterine rupture. Here is the exact quote:
The overall risk of perinatal death due to uterine rupture was 6.2 percent. The two studies of women delivering at term that reported perinatal death rates report that 0 to 2.8 percent of all uterine ruptures resulted in a perinatal death (Guise 2010).
In other words, of the women who had uterine ruptures, 6.2% (1 in 16) resulted in infant deaths. When we limited the data to women delivering at term, as opposed to babies of all gestational ages, the risk was as high as 2.8 (1 in 36)%.
When we look at the overall risk of an infant death during a trial of labor after cesarean, the NIH reported the rate of 0.13%, which works out to be one infant death per 769 trials of labor.
The source of the confusion
The problem with this statistic is that some people have misinterpreted it to mean that only 6% of ruptures are true, complete uterine ruptures. In other words, if we take the 0.4% (1 in 240) uterine rupture rate (Landon, 2004), they believe that only 6% of those ruptures or 0.024% (1 in 4166) are true, complete ruptures. This is false. The 0.4% uterine rupture statistic measured true, complete, uterine ruptures in spontaneous labors after one prior low, transverse (“bikini cut”) cesarean.
So how many dehiscences did Landon (2004) detect? Landon reported a 0.7% uterine rupture rate and a 0.7% dehiscence rate. (Note that these statistics include a variety of scar types as well spontaneous, augmented, and induced labors.) So Landon found that dehiscence occurs at the same rate as uterine rupture.
I think the best way to avoid confusion is to use very clear language: 6.2% (1 in 16) of uterine ruptures result in an infant death. Put another way, for every 16 uterine ruptures, there will be one baby that dies.
Elapsed time and infant death
What determines if a baby dies or has brain damage? Some research on infant cord blood gases has suggested that if the baby isn’t delivered (almost always by CS) within 16 – 17 minutes of a uterine rupture, there can be serious brain damage or death to baby. You can watch a presentation from the 2010 NIH VBAC Conference entitled “The Immediately Available Physician Standard” by Howard Minkoff, M.D. for more information or read his presentation abstract.
Now you know the difference between uterine rupture, uterine dehiscence and the meaning of the 6% statistic. It’s helpful to understand the terminology used in relation to uterine rupture otherwise it can be very confusing as you wade your way through the statistics! It’s also very important for people to use specific words whose definitions are clear instead of words such as “catastrophic” that could mean multiple things.
Afterward – The big picture
The following are excerpts from the Evidence Report (Guise 2010) , the 400 page evidence report assembled for the 2010 NIH VBAC Conference. The limitation of Guise (2010) is that these stats are for all VBACs – all scar types, multiple prior cesareans, induced/augmented labors, etc. It would have been helpful if they had broke out the data in these ways.
While rare for both TOL [trial of labor] and ERCD [elective repeat cesarean delivery], maternal mortality was significantly increased for ERCD at 13.4 per 100,000 versus 3.8 per 100,000 for TOL. The rates of maternal hysterectomy, hemorrhage, and transfusions did not differ significantly between TOL and ERCD. The rate of uterine rupture for all women with prior cesarean is 3 per 1,000 and the risk was significantly increased with TOL (4.7 1,000 versus 0.3 1,000 ERCD). Six percent of uterine ruptures were associated with perinatal death.” Perinatal death due to UR from term studies was 2.8%. “Perinatal mortality was significantly increased for TOL at 1.3 per 1,000 versus 0.5 per 1,000 for ERCD… VBAC is a reasonable and safe choice for the majority of women with prior cesarean. Moreover, there is emerging evidence of serious harms relating to multiple cesareans… The occurrence of maternal and infant mortality for women with prior cesarean is not significantly elevated when compared with national rates overall of mortality in childbirth. The majority of women who have TOL will have a VBAC, and they and their infants will be healthy. However, there is a minority of women who will suffer serious adverse consequences of both TOL and ERCD. While TOL rates have decreased over the last decade, VBAC rates and adverse outcomes have not changed suggesting that the reduction is not reflecting improved patient selection.
A systematic review strives to be patient-centered and to provide both patients and clinicians with meaningful numbers or estimates so they can make informed decisions. Often, however, the data do not allow a direct estimate to calculate the numbers that people desire such as the number of cesareans needed to avoid one uterine rupture related death. The assumptions that are required to make such estimates from the available data introduce additional uncertainty that cannot be quantified. If we make a simplistic assumption that 6 percent of all uterine ruptures result in perinatal death (as found from the summary estimate), the range of estimated numbers of cesareans needed to be performed to prevent one uterine rupture related perinatal death would be 2,400 from the largest study,204 and 3,900-6,100 from the other three studies of uterine rupture for TOL and ERCD.10, 97, 205 Taken in aggregate, the evidence suggests that the approximate risks and benefits that would be expected for a hypothetical group of 100,000 women at term gestational age (GA) who plan VBAC rather than ERCD include: 10 fewer maternal deaths, 650 additional uterine ruptures, and 50 additional neonatal deaths. Additionally, it is important to consider the morbidity in future pregnancies that would be averted from multiple cesareans particularly in association with placental abnormalities.