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Vaginal Birth After Cesarean
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4. Risk of uterine rupture
Case scenario #3
R. I. is a 37 y/o G8P6 at 39 weeks gestation who presents in active labor to your facility, where cesarean capability is available. She has a history of having had four normal vaginal births followed by a cesarean for her fifth child because of a transverse lie with ruptured membranes. She then had a V.B.A.C. with her sixth child and would like to have another normal delivery now. She is uncomfortable with contractions. On exam you estimate the fetal weight at 8 pounds and find her cervix to be 6-7 cm dilated, 80% effaced, with the vertex at 0 station and intact membranes. The fetal monitoring strip reveals several recurrent variable decelerations but good beat-to-beat variability.
How would you counsel her?
What is the clinical picture of uterine rupture?
What are the risk factors for uterine rupture in women entering labor with a prior cesarean? Several scoring systems have been devised to try to answer this question, but none have great sensitivity or specificity although they do identify pertinent risk factors. The most clinically relevant study looking at this question comes from U.S.C.-Los Angeles County Medical Center, where, until the recent past, over 15,000 deliveries a year were attended, the majority occurring to women recently immigrated from Mexico with very little in the way of past obstetric records.
Leung #1 looked at 99 uterine ruptures occurring at their institution and found the overall rupture rate for T.O.L.A.C. was 0.8% for women with one prior cesarean, but rose to 3.7% (OR=2.6) for those with more than one prior operation.* "Excessive" oxytocin (defined as oxytocin begun at <4 cm dilation and continued until birth) had an OR of 2.7 for uterine rupture. Most significantly, dysfunctional (i.e., non-progressive) labor had an OR of 7.2 for uterine rupture, and almost all these women also received oxytocin augmentation.
The clinical signs of actual uterine rupture were not those classically described in the textbooks. Excessive pain and vaginal bleeding were seen in less than 15% of the cases, loss of the uterine pressure tracing in none, and recession of the presenting part in only 6%. Leung #2
Of greatest predictive value were fetal heart rate abnormalities, usually repetitive lates and/or variables, which were found in 78% of the cases. There was one maternal death and 6 perinatal deaths; 6 other infants survived with severe neurologic damage.
Risks factors for uterine rupture
Data on uterine rupture are difficult to analyze since various terminologies have been used. Some authors do not distinguish between uterine defects that have no maternal/fetal consequences (asymptomatic uterine rupture, dehiscence, incomplete rupture) and those associated with bleeding, extrusion of the fetus, or fetal heart rate abnormalities (complete rupture).
Symptomatic uterine rupture occurs in 0-7.8 per 1,000 trials of labor. This represents an additional risk of rupture with trial of labor over elective repeat cesarean delivery of 2.7 per 1,000. The most common factors protective of scar integrity in a TOLAC delivery are previous successful vaginal delivery and a thick lower uterine segment. A previous VBAC reduced the risk of uterine rupture by 75% or more. The risk of intrapartum uterine rupture was higher among women who had not previously given birth vaginally. Previous vaginal delivery was also associated with the decreased risk of perinatal death due to uterine rupture.
In the only study that controlled for other potential confounding variables, the risk of uterine rupture during labor was nearly 5 times greater for women with 2 previous cesarean deliveries when compared with women who had 1 previous cesarean delivery. Women with a previous vaginal delivery followed by a cesarean delivery were only approximately one fourth as likely to sustain uterine rupture during a trial of labor. Therefore, for women with 2 prior cesarean deliveries, only those with a prior vaginal delivery should be considered candidates for a spontaneous trial of labor. A trial of labor is not recommended in patients at high risk for uterine rupture. Circumstances under which a trial of labor should not be attempted are listed on page 3
Decisions about uterine rupture risk levels can help triage levels of care needed for individual trial of labor after cesarean (TOLAC) patients. Symptomatic uterine rupture typically refers to non-surgical complete disruption of all uterine layers, usually with bleeding and sometimes with extrusion of part or all of the fetal-placental unit. It is often associated with maternal and/or fetal morbidity and mortality. Management: Facility location and resources
Previous closed uterine evacuation is not associated with uterine rupture in VBAC. A trial of labor is not recommended in patients at high risk for uterine rupture. Circumstances under which a trial of labor should not be attempted include previous classical or T-shaped incision or extensive transfundal uterine surgery, or previous uterine rupture.
'17 Minute Rule' vs '30 Minute Rule'
All the infants that died were extruded from the uterus into the abdominal cavity, and--of special clinical significance--all the deaths, and all the neurologic injuries, occurred if the time from suspicion of rupture to delivery exceeded 17 minutes. Leung #2. Perhaps this time period should now define "a reasonable time period" to effect an emergent cesarean, rather than using a "30 minute rule."
* NB: 'Two prior uterine scars and no vaginal deliveries' is listed as a circumstance under which trial of labor should not be attempted by the American College of Obstetricians and Gynecologists ACOG Practice Bulletin No. 54, 'Vaginal birth after previous cesarean delivery'.
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