Birth intervals & uterine rupture aka how long to wait to VBAC
Reader Susanne asks:
Hi. I’m new to your site and just trying to get some more info on VBAC. My daughter was a normal vaginal delivery. My second pregnancy (a surrogate pregnancy) was also a normal vaginal delivery. My third (also a surrogate pregnancy) was twins. I had planned to attempt a vaginal delivery with the twins with the support of my OB as long as Baby A was head down. Unfortunately she was breech and I ended up with a c-section at 36 1/2 weeks. My OB said if I want to attempt a VBAC for my next pregnancy I need to wait at least 2 years between the c-section and getting pregnant again. Is she just being cautious? Or is it really necessary to wait 2 years?
Let’s first start with what ACOG says. ACOG’s VBAC guidelines associate short birth intervals with lower VBAC rates, but they do not mention a connection between short birth intervals and increased rates of uterine rupture. Short birth intervals are not a contraindication to VBAC. That is because the available evidence has not made a solid connection between short birth intervals and uterine rupture.
So let’s look at some of the evidence on uterine rupture by birth interval. One thing to be aware of when reading birth interval research is that studies are not always measuring the same thing. It’s really important to look at the specific language they use so you understand exactly what they are measuring.
Some studies refer to the interdelivery interval. This is the time from your last delivery to your next delivery, or birth to birth. Other studies measure the interpregnancy interval which is from birth to conception.
Two more things to know before we dive in:
- Induction and augmentation increase the risk of uterine rupture.
- When we measure events like uterine rupture, we need ideally a couple thousand people in order to accurately capture and measure this uncommon event.
So, let’s look at our first study. Bujold (2002) looked at women who had a VBAC less than 12 months after their cesarean. Bujold was examining the interdelivery interval.
It found a 4.8% uterine rupture rate. Now this number looks really big because it is. But let’s look at the fine print.
First, there were only 21 women included in this category – not nearly enough to accurately measure rare events – and 52% of them were induced or augmented.
Here is the challenge with that finding… people, specifically providers and administrators, will quickly look at his study, and often just read the abstract, and see this highly elevated rupture rate associated with short birth intervals and create policy saying that only women with a specified number of months between their cesarean and VBAC can plan a VBAC.
But the problem is that the abstract often does not include important context like sample sizes and induction/augmentation rates. It is important to read the find print.
Let’s move to Stamilio (2007) which examined interpregnancy intervals and reported a 3.1% rate of rupture among women who conceived less than 6 months after their cesarean. Let’s look at the fine print: 286 women, 68% of them induced. Again, very difficult to determine if that elevated rupture rate is from short birth intervals, small sample sizes, or high rates of induction/augmentation.
So does this mean it doesn’t matter when a person gets pregnant? Well, not quite.
Stamilio (2007) stated,
“We hypothesized that short interpregnancy intervals may lead to altered wound healing and an increased risk of uterine rupture in patients who attempt a vaginal birth after cesarean. Our hypothesis is based on previous observational studies that suggest an association between short birth interval and increased adverse perinatal outcomes and wound-healing research that indicates that uterine smooth muscle tissue repair evolves over several months…. Importantly, there is radiographic and hysteroscopic evidence that cesarean scar development is incomplete as long as 6 or 12 months postoperatively.”
In other words, the uterine scar is still healing and changing 6 to 12 months after a cesarean.
Bujold (2002) states that “the scar may require [less than or equal to] ≤ 24 months to reach its full strength.” He cited another study which used an MRI machine to measure incision healing after a cesarean delivery. That study found that “at least 6 months were needed for the zonal anatomy of the uterus to reappear completely.” Another study noted that smooth muscle regeneration “takes place slowly and meagerly.”
Bujold (2002) hypothesizes,
“Shrinking of the newly developed connective tissue is followed by smooth muscle regeneration, which results in an eventual normal relationship of smooth muscle and connective tissue. Perhaps as the smooth muscle progressively forms and approaches this normal relationship, the strength of the scar increases.“
It’s because the evidence on uterine rupture by birth interval is weak due to small sample sizes and high rates of induction/augmentation that ACOG does not risk out those with short birth intervals for VBAC.
So how long should parents wait to get pregnant again? The range 18 -24 months between pregnancies (delivery to conception) is the general recommended interval regardless of mode of delivery.
It’s not just about the physical recovery from delivery (vaginal or cesarean.) It’s about the general stress and strain on our bodies and minds from the pregnancy, delivery, breastfeeding, and then caring for an infant. Really short or really long intervals are associated with higher complication rates independent of VBAC.
It will be great if/when larger studies are conducted so we have a better idea of the risk differential, if any, between short and long birth intervals.
Does that mean that you should have a repeat cesarean if you get pregnant sooner? That’s not what ACOG, or the evidence, points to.
Right now, we don’t have solid evidence that connects short birth intervals with increased rates of uterine rupture.
Also keep in mind that since you have two prior vaginal births, your likelihood of VBAC success increases to over 85% (Landon, 2005).
If you want to dive into more studies about this topic and others so you can understand the facts, check out my online VBAC prep course, “The Truth About VBAC for Families.”
Best of luck with your decision!
Bujold, E., Mehta, S., Bujold, C., & Gauthier, R. (2002). Interdelivery interval and uterine rupture. American Journal of Obstetrics & Gynecology, 187(5), 1199-1202.
Landon, M. B., Leindecker, S., Spong, C., Hauth, J., Bloom, S., Varner, M., & Moawad, A. (2005). The MFMU Cesarean Registry: Factors affecting the success of trial of labor after previous cesarean delivery. American Journal of Obstetrics & Gynecology, 193(3), 1016-1023.
Stamilio, D. M., DeFranco, E., Pare, E., Odibo, A. O., Peipert, J. F., Allsworth, J. E., et al. (2007). Short Interpregnancy Interval: Risk of Uterine Rupture and Complications of Vaginal Birth After Cesarean Delivery. Obstetrics & Gynecology, 110 (5), 1075-1082.
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As an internationally recognized consumer advocate and Founder of VBAC Facts®, Jen helps perinatal professionals, and cesarean parents, achieve clarity on vaginal birth after cesarean (VBAC) through her educational courses for parents, online membership for professionals, continuing education trainings, and consulting services. She speaks at conferences across the US, presents Grand Rounds at hospitals, advises on midwifery laws and rules that limit VBAC access, educates legislators and policy makers, and serves as an expert witness and consultant in legal proceedings. She envisions a time when every pregnant person seeking VBAC has access to unbiased information, respectful providers, and community support, so they can plan the birth of their choosing in the setting they desire.