Myth: 50% of uterine ruptures occur before labor
Becky recently ask this question:
I read somewhere that the risk of uterine rupture is actually higher during pregnancy than during birth. Does anyone have a source for this?
I had heard the same thing many times. However, no one who shared this stat with me could ever cite a study substantiating it. I looked and looked on and off for years and never found it.
Instead, I found “Uterine rupture in the Netherlands: a nationwide population-based cohort study” (Zwart, 2009), “the largest prospective report of uterine rupture in women without a previous cesarean in a Western country.” Zwart differentiated between uterine rupture and dehiscence and included 97% of births in The Netherlands between August 1, 2004 and August 1, 2006. All told, Zwart studied 358,874 total deliveries, 25,989 of which were TOLACs.
I have referenced Zwart before when comparing scarred vs. unscarred rupture rates and scarred vs. induced, unscarred rupture rates. Zwart also included data on pre-labor rupture which I will share with you as well.
Scar rupture before labor
Zwart reported that 9% (1 in 11) of scar ruptures (women with prior cesareans) happened before the onset of labor. When we take 9% of the overall scar rupture rate of 0.64% (1 in 156)*, we get a 0.0576% (1 in 1736) risk of a scar rupture before labor.
Unscarred rupture before labor
Zwart (2009) found 16% (1 in 6.25) of ruptures in women without prior cesareans (unscarred ruptures) occurred before labor and an overall unscarred rupture rate of 0.007% (1 in 14,286)*. When we multiply these two numbers, we get a 0.00112% (1 in 89,286) risk of uterine rupture in an unscarred uteri before labor.
Here is a table comparing the numbers:
|Overall UR Rate||% of URs that Occur Pre-Labor||Pre-Labor UR Rate|
The war of the studies
Remember, all these stats are based on one study. Other studies might find different rates. However, I think Zwart would have the most accurate rates to date as it is “the largest prospective report of uterine rupture in women without a previous cesarean in a Western country.” This is an important factor because uterine rupture in an unscarred woman is an extremely rare event. We need tens of thousands of women in order to get an accurate number. The fact that Zwart includes over 300,000 unscarred women is huge.
Take home message: The risk of uterine rupture before labor is extremely rare especially for unscarred women.
* This statistic includes non-induced/augmented, induced, and augmented labors.
Zwart, J. J., Richters, J. M., Ory, F., de Vries, J., Bloemenkamp, K., & van Roosmalen, J. (2009, July). Uterine rupture in the Netherlands: a nationwide population-based cohort study. BJOG: An International Journal of Obstetrics and Gynaecology, 116(8), pp. 1069-1080. Retrieved January 15, 2012, from http://onlinelibrary.wiley.com/doi/10.1111/j.1471-0528.2009.02136.x/full
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Jen Kamel is the founder of VBAC Facts, an educational, training and consulting firm. As a nationally recognized VBAC strategist and consumer advocate, she has been invited to present Grand Rounds at a hospital, served as an expert witness in a legal proceeding, and has traveled the country educating hundreds of professionals and highly motivated parents. Even more have accessed her trainings online. She speaks at national conferences and has worked as a legislative consultant in various states focusing on midwifery legislation and regulations. She has testified multiple times in front of the California Medical Board and legislative committees on the importance of VBAC access and is the Secretary for the California Association of Midwives and the California Association of Licensed Midwives. Her favorite flavor of ice cream is peanut butter chocolate. And mint chip. And coffee.