Risk of Uterine Rupture

Here is an interesting study from Canada, published in 2002, which discusses the risk of uterine rupture over the course of ten years. There were almost 115,000 births in this study, with about 10% after a prior C-section. Nearly 40% of these women attempted a C-section and 80% of them had a successful vaginal birth. Of the total number of births, there were 39 uterine ruptures.

When they say “uterine rupture”, that sounds really bad, and it can be, but they class “complete” uterine ruptures in with “incomplete” uterine ruptures, also called “dehiscence.” They said, “Uterine dehiscence was associated with minimal maternal and perinatal morbidity.” There were 18 complete ruptures and 21 incomplete. This is something to keep in mind while reading other studies — whether they differentiate between complete and incomplete ruptures, because the cases of dehiscence had much better outcomes than those of complete rupture.

Three of the complete ruptures and none of the dehiscence were in unscarred uteri — two were after a previous D&C for a miscarriage and one was in a woman with no previous uterine surgery. (Since the only examples I could find of uterine ruptures in unscarred uteri were attributed to agents used to induce or augment labor, I will assume that that is what happened in these three cases. However, it says later that there was “no labor” in several cases of rupture and dehiscence, including one with an unscarred uterus. If anyone knows of an incident of uterine rupture or dehiscence in an unscarred uterus with spontaneous labor, or with no labor at all — no induction or augmentation — please let me know. I’ve heard of being so “great with child” that you feel like you’re about to pop, but I’ve never actually heard of it happening.)

The remainder (36) were all in women who had had a previous C-section. There were 4 ruptures and 10 incidents of dehiscence among women who did not labor; and 11 ruptures and 11 incidents of dehiscence in women attempting a VBAC. Wait a second — I’m confused. As I’m typing this, I have a pretty bad cold, so perhaps that is interfering with my reading and comprehension, but when I look at this table of the incidence of uterine rupture, it shows 21 dehiscence among women with a previous C-section, but only 11 among a VBAC attempt. However, when I look at this table of the characteristics of labor, it shows the following rates of dehiscence among various types of labor: for spontaneous, 9; induction, 6; no labor, 6. So, how is it that “Ten women (four complete, six dehiscence) had no labor,” when according to the other chart, 11 of the dehiscence were in VBAC attempts? Eleven plus six equals seventeen, right? Yet there were 21 dehiscence? Perhaps the other 4 were in women who went into spontaneous labor prior to a scheduled C-section, so it was not properly a “VBAC attempt”? Obviously women who choose a repeat C-section would not be induced, so we must then assume that 4 of the 9 “spontaneous” were elective repeat C-sections. Yet it said they had no labor. If someone wants to shine a light into this, please feel free.

But this throws things off. Very frustrating! So it’s debatable whether these 4 dehiscence that were not in “no labor” nor in the “VBAC attempts” were due to spontaneous labor prior to a planned C-section, or if they happened prior to the onset of labor, like the other six. And if the complete uterine rupture in an unscarred uterus “with no labor” was not an induction of labor, I’d really like to know, because I’ve not heard of this happening before. It seems like it would be the subject of a case study or something if it happened, because it is so rare. Is it possible, then, that in this “no man’s land” between spontaneous labor and “no labor” there were inductions which were begun, and halted prior to the establishment of labor, perhaps due to fetal distress?

Moving on…

There were 103,348 births to women who had not had a previous C-section, with 3 uterine ruptures, all complete, for an incidence of 0.029/1000 ruptures. Of the remaining 15 complete ruptures among women who had had previous C-sections, 11 were during a VBAC attempt. Which sounds like 4 complete ruptures happened in a scarred uterus with no labor; yet as I’ve previously pointed out, of the 4 such ruptures, 1 was in an unscarred uterus, which means that there were 3 ruptures with no labor and 1 with some labor. Which is confusing because it sounds like they’re saying two different things about the same incident.

There was one stillbirth, which happened in one of the women with an unscarred uterus (previous D&C), with “spontaneous onset of labor” — whether that excludes augmentation of labor is not said. Again, this may be an indication of drugs used to augment labor causing uterine rupture even in an unscarred uterus. It’s also possible that the previous D&C damaged her uterus — perhaps even punctured it, although that is a rare occurrence — and then spontaneous labor broke the hole wide open.

There were no neonatal deaths in the women who had dehiscence, and three in women who had complete ruptures. However, two neonatal deaths were due to lethal anomalies, with only one due to severe asphyxia in a woman with spontaneous labor. This chart compares outcomes between dehiscence and complete rupture, but doesn’t have outcomes of babies with women who did not have uterine ruptures, whether planned or unplanned C-sections nor successful vaginal births or VBACs. Obviously, the rate of adverse circumstances is higher with a complete uterine rupture than with an dehiscence. The study says,

Dehiscence of a previous cesarean scar is much less traumatic, and 52% of our patients were without symptoms and discovered en passant only at the time of repeat cesarean delivery. The perinatal outcome with dehiscence was almost universally good with no serious sequelae. However, with complete uterine rupture there was, excluding lethal anomalies, one perinatal death, one-third of neonates with severe asphyxia, but no infants with long-term postasphyctic sequelae in 4516 VBAC attempts.

So, according to the “Incidence of Uterine Rupture” chart, there were 4 ruptures that were not VBAC attempts (0.566/1000), and 11 that were (2.4/1000), with a total rupture rate post-C-section of 1.3/1000. Compared to a total rupture rate among women with non-scarred uteri of 3/103,348, or 0.029/1000.

The perinatal outcome with dehiscence was almost universally good with no serious sequelae. However, with complete uterine rupture there was, excluding lethal anomalies, one perinatal death, one-third of neonates with severe asphyxia, but no infants with long-term postasphyctic sequelae in 4516 VBAC attempts.

So, there was 1 death out of 4516 attempts. or a rate of 0.22/1000.

While the researchers noted whether the women had more than one C-section, or whether the scar was horizontal or vertical (all of the ruptures in the “vertical scar” group were complete — there were no cases of dehiscence; but I would like to know the failure rate of such scars, since not all vertical scars do give way), it didn’t note whether the uterus was closed in a single layer or a double layer. That may make a difference in the rate of future uterine rupture. Spacing of pregnancies may also make a difference, with close pregnancies increasing the risk of uterine rupture in a subsequent VBAC attempt.

Oxytocin induction was used in 2 complete ruptures and 4 dehiscence; oxytocin augmentation was used in 3 complete ruptures and 0 dehiscence. Prostin (a vaginal suppository with a prostaglandin) was used in 1 complete rupture and 2 dehiscence.

…the fact that oxytocic agents for induction or augmentation of labor were involved in 43% of complete and 40% of dehiscence highlights the potential risk.

Misoprostol (miso, cytotec), is not mentioned in this study, and one thing I read recently said that American OBs didn’t start using it until 1996; and since this study concluded in 1997, I assume it wasn’t used at all in this study.

3 Responses

  1. I have read a story of a 2nd time mom (no cesarean – so I am assuming an unscarred uterus) This mom was a Bradley Instructor and her birthing time began, all was well as she was laboring at home and suddenly extreme pain and she knew something was wrong. She went in and had to have emergency cesarean because her uterus had ruptured.

    This was the first and only time I have heard of this happening. But apparantly it does.

  2. […] videos woman ecstatic hospitalKick Counts — Fetal MovementBreech Home Birth After CesareanRisk of Uterine RuptureLots of Birth VideosHow many times CesareanOne of life’s […]

  3. […] includes both complete and incomplete ruptures, and in one large study I’ve blogged about before, there were greater or equal instances of incomplete uterine rupture ( which “was associated […]

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