Uterine rupture in pregnancy

When the studies were limited to a subset of 8 thatprovided data about the spontaneous rupture of unscarred uteri in developed countries, the rate was 1 per 8,434 pregnancies 0.012%.Cong

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2,951,297 pregnant women, yielding an overall uterine rupture rate of 1 in 1,146 pregnancies (0.07%)

The initial signs and symptoms of uterine rupture are typically nonspecific, which makes the diagnosis difficult and sometimes delaysdefinitive therapy From the time of diagnosis to delivery, generally only 10-37 minutes are available before clinically significant fetal

morbidity becomes inevitable Fetal morbidity occurs as a result of catastrophic hemorrhage, fetal anoxia, or both

The premonitory signs and symptoms of uterine rupture are inconsistent, and the short time for instituting definitive therapeutic actionmakes uterine rupture in pregnancy a much feared event for medical practitioners

Protrusion or expulsion of the fetus and/or placenta into the abdominal cavity

Need for prompt cesarean delivery

Uterine repair or hysterectomy

In contrast to frank uterine rupture, uterine scar dehiscence involves the disruption and separation of a preexisting uterine scar Uterinescar dehiscence is a more common event than uterine rupture and seldom results in major maternal or fetal complications

Importantly, when the defect in the uterine wall is limited to a scar dehiscence, it does not disrupt the overlying visceral peritoneum and itdoes not result in clinically significant bleeding from the edges of the pre-existing uterine scar In addition, in cases of uterine dehiscence(as opposed to uterine rupture), the fetus, placenta, and umbilical cord remain contained within the uterine cavity If cesarean delivery isneeded, it is for other obstetrical indications and not for fetal distress attributable to the uterine disruption

Although a uterine scar is a well-known risk factor for uterine rupture (most of which arise from prior cesarean delivery), the majority ofevents involving the disruption of uterine scars result in uterine scar dehiscence rather than uterine rupture These two entities must beclearly distinguished, as the options for clinical management and the resulting clinical outcomes differ significantly

Sources of information and study selection

The peer-reviewed literature was searched using the PubMed, Medline, and Cochrane databases for all relevant articles published in theEnglish language The search terms were uterine rupture, pregnancy and prior cesarean section, vaginal birth after cesarean, VBAC, trial

of labor (TOL), trial of labor after cesarean (TOLAC), uterine scar dehiscence, and pregnancy and myomectomy Standard reference

tracing was also used

Articles published from 1976 through May, 2012 that described the incidence of uterine rupture and that included sufficient informationregarding the authors' definitions of uterine rupture and of uterine scar dehiscence were incorporated for review All studies were

observational or reviews A total of 133 published articles were included for data extraction and analysis

Incidence and risk factors

Meta-analysis of pooled data from 25 studies in the peer-reviewed medical literature published from 1976-2012 indicated an overall

incidence of pregnancy-related uterine rupture of 1 per 1,416 pregnancies (0.07%) When the studies were limited to a subset of 8 thatprovided data about the spontaneous rupture of unscarred uteri in developed countries, the rate was 1 per 8,434 pregnancies (0.012%).Congenital uterine anomalies, multiparity, previous uterine myomectomy, the number and type of previous cesarean deliveries, fetal

macrosomia, labor induction, uterine instrumentation, and uterine trauma all increase the risk of uterine rupture, whereas previous

successful vaginal delivery and a prolonged interpregnancy interval after a previous cesarean delivery may confer relative protection In

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contrast to the availability of models to predict the success of a vaginal delivery after a TOLAC, accurate models to predict the specific risk of uterine rupture in individual cases are not available

person-The major patient characteristics for determining the risk of uterine rupture are noted below

Uterine status is either native (unscarred) or scarred Scarred status may include previous cesarean delivery, including the following:

Single low transverse (further subcategorized by 1-layer or 2-layer hysterectomy closure)

Single low vertical

Classic vertical

Multiple previous cesarean deliveries

Scarred status may also include previous myomectomy (transabdominal or laparoscopic)

Uterine configuration may be normal or may involve a congenital uterine anomaly

Pregnancy considerations include the following:

Grand multiparity

Maternal age

Placentation (accreta, percreta, increta, previa, abruption)

Cornual (or angular) pregnancy

Uterine overdistension (multiple gestation, polyhydramnios)

Dystocia (fetal macrosomia, contracted pelvis)

Gestation longer than 40 weeks

Trophoblastic invasion of the myometrium ( hydatidiform mole, choriocarcinoma)

Previous pregnancy and delivery history may include the following:

Previous successful vaginal delivery

No previous vaginal delivery

Interdelivery interval

Labor status is determined as follows:

Not in labor

Spontaneous labor

Induced labor - with oxytocin, with prostaglandins

Augmentation of labor with oxytocin

Duration of labor

Obstructed labor

Obstetric management considerations include the following:

Instrumentation ( forceps use)

Intrauterine manipulation (external cephalic version, internal podalic version, breech extraction, shoulder dystocia, manual extraction

of placenta)

Fundal pressure

Uterine trauma includes the following:

Direct uterine trauma (eg, motor vehicle accident, fall)

Violence (eg, gunshot wound, blunt blow to abdomen)

Rupture of the Unscarred Uterus

The normal, unscarred uterus is least susceptible to rupture Grand multiparity, neglected labor, malpresentation, breech extraction, anduterine instrumentation are all predisposing factors for uterine rupture A 10-year Irish study by Gardeil et al showed that the overall rate ofunscarred uterine rupture during pregnancy was 1 per 30,764 deliveries (0.0033%) No cases of uterine rupture occurred among 21,998primigravidas, and only 2 (0.0051%) occurred among 39,529 multigravidas with no uterine scar. [1]

A meta-analysis of 8 large, modern (1975-2009) studies from industrialized countries revealed 174 uterine ruptures among 1,467,534deliveries This finding suggests that the modern rate of unscarred uterine rupture during pregnancy is 0.012% (1 in 8,434) This rate ofspontaneous uterine rupture has not changed appreciably over the last 50 years, and most of these events occur at term and during labor

An 8-fold increased incidence of uterine rupture of 0.11% (1 in 920) has been noted in developing countries, with this increased incidence

of uterine rupture having been attributed to a higher-than-average incidence of neglected and obstructed labor due to inadequate access tomedical care

When the risk of uterine rupture for women with different types of risk factors is assessed, these baseline rates of pregnancy-related

uterine rupture in women with native, unscarred uteri, specifically, the rates of 0.012% (1 in 8,434) for women living in industrialized

countries and 0.11% (1 in 920) for women living in developing countries, represent observational benchmarks that should be referenced forall comparisons

Effect of maternal parity

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Many authors have considered multiparity a risk factor for uterine rupture Golan et al noted that, in 19 of 61 cases (31%), uterine ruptureoccurred in women with a parity of more than 5. [2] Schrinsky and Benson found that 7 of 22 women (32%) who had unscarred uterinerupture had a parity of greater than 4. [3] In a study by Mokgokong and Marivate, the mean parity for women who had pregnancy-relateduterine rupture was 4. [4] Despite the apparent increase in the risk of uterine rupture associated with high parity, Gardeil et al found only 2women with uterine rupture among 39,529 multigravidas who had no previous uterine scar (0.005%). [1]

Rupture of the unscarred uterus before labor versus during labor

Schrinsky and Benson reported 22 cases of uterine rupture in gravidas with unscarred uteri Nineteen occurred during labor (86%), and 3occurred before labor (14%) This percentage was markedly different from that of gravidas with a previous uterine scar, for whom thetiming of uterine rupture between labor and the antepartum period was nearly evenly distributed. [3]

Oxytocin augmentation and induction of labor in the unscarred uterus

The use of oxytocin for labor augmentation versus labor induction is often quite different The two patient populations widely vary in theirkey attributes, as well as in the oxytocin doses that are typically given, which systematically varies between the two groups Despite this,many investigations concerning the use of oxytocin and the risk of uterine rupture have failed to make this distinction

In 1976, Mokgokong and Marivate reported 260 uterine ruptures among 182,807 deliveries that involved unscarred uteri, and 32 of the 260(12%) were associated with oxytocin use. [4] Rahman et al similarly found that oxytocin was administered in 9 of 65 cases (14%) that

involved unscarred uterine rupture. [5] Golan et al noted that, among 126,713 deliveries, oxytocin was used in 26 of 61 cases (43%) thatinvolved unscarred uterine rupture. [2] However, Plauche et al attributed only 1 of 23 unscarred uterine ruptures (4%) to the use of oxytocin

[6]

Based on this type of limited information, the increased risk of uterine rupture attributable to the use of oxytocin in gravidas with unscarreduteri is uncertain However, women who have had a cesarean delivery appear to have an increased risk of uterine rupture associated withthe use of oxytocin, both when it is used for labor augmentation and labor induction (see Table 1)

Congenital uterine anomalies

In a review article, Nahum reported that congenital uterine anomalies affect approximately 1 in 200 women. [7] In such cases, the walls ofthe abnormal uteri tend to become abnormally thin as pregnancies advance, and the thickness can be inconsistent over different aspects

of the myometrium (uterine musculature). [8, 9, 10, 11]

Ravasia et al reported an 8% incidence of uterine rupture (2 of 25) in women with congenitally malformed uteri compared with 0.61% (11 of

1,788) in those with normal uteri (P =.013) who were attempting VBAC. [12] Both cases of uterine rupture in the women with uterine

anomalies involved labor induction with prostaglandin E2

In contrast, a study of 165 patients with Müllerian duct anomalies who underwent spontaneous labor after 1 prior cesarean delivery

reported no cases of uterine rupture. [13] Of note, in this study 36% (60 of 165) had only a minor uterine anomaly (arcuate or septate

uterus), and 64% (105 of 165) had a major uterine anomaly (unicornuate, didelphys, or bicornuate uterus) Moreover, only 6% (10 of 165)

of patients with Müllerian duct anomalies underwent induction of labor

For pregnancies that implant in a rudimentary horn of a uterus, a particularly high risk of uterine rupture is associated with the induction oflabor (≤ 81%; 387 of 475 cases). [14] Importantly, 80% of ruptures involving these types of rudimentary horn pregnancies occurred beforethe third trimester, with 67% occurring during the second trimester

The decision for induction of labor in women with a congenitally anomalous uterus, especially in cases of a previous cesarean delivery,must be carefully considered, given the higher incidence of uterine rupture reported in this patient population Although the uterine rupturerate for unscarred anomalous uteri during pregnancy is increased relative to that for normal uteri, the precise increase in risk associatedwith the different types of uterine malformations remains uncertain

Previous Uterine Myomectomy and Uterine Rupture

Previous myomectomy by means of laparotomy

Nearly all uterine ruptures that involve uteri with myomectomy scars have occurred during the third trimester of pregnancy or during labor.Only 1 case of a spontaneous uterine rupture has been reported before 20 weeks of gestation. [15] Brown et al reported that among 120term infants delivered after previous transabdominal myomectomy, no uterine ruptures occurred, and 80% of the infants were deliveredvaginally. [16] In contrast, Garnet identified 3 uterine ruptures among 83 women (4%) who had scars from a previous myomectomy and whounderwent elective cesarean delivery because of previous myomectomy. [17]

Such reports do not often delineate the factors that were deemed important for assessing the risk of subsequent uterine rupture (eg,

number, size, and locations of leiomyomata; number and locations of uterine incisions; entry of the uterine cavity; type of closure

technique) Further studies to investigate these issues are needed

Previous laparoscopic myomectomy

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Dubuisson et al reported 100 patients who underwent laparoscopic myomectomy and found 3 uterine ruptures during subsequent

pregnancies. [18] Only 1 rupture occurred at the site of the previous myomectomy scar, resulting in the conclusion that the risk of

pregnancy-related uterine rupture attributable to laparoscopic myomectomy is 1% (95% CI, 0-5.5%) However, the rarity of spontaneousuterine rupture raises the issue of whether the 2 uterine ruptures at sites that were not coincident with previous myomectomy scars wereattributable to the previous myomectomies If so, a markedly higher 3% uterine rupture rate is associated with previous laparoscopic

myomectomy

Different authors reported no pregnancy-related uterine ruptures in 4 studies of 320 pregnancies in women who previously underwentlaparoscopic myomectomy. [19, 20, 21, 22] However, in all 4 studies, the number of patients who were allowed to labor was low, and a highpercentage of deliveries were by scheduled cesarean delivery (80%, 79%, 75%, and 65%, respectively)

In a prospective study from Japan, there were no uterine ruptures among 59 patients with a successful vaginal delivery after a prior

laparoscopic myomectomy. [23] In a multicenter study in Italy with 386 patients who achieved pregnancy after laparoscopic myomectomy,there was 1 recorded spontaneous uterine rupture at 33 weeks' gestation (rupture rate 0.26%). [24]

Uterine rupture has been reported to occur as late as 8 years after laparoscopic myomectomy. [25] This finding suggests that additionalinvestigations with long-term follow-up are needed

Rupture of the Scarred Uterus Due to Previous Cesarean Delivery

The effect of previous cesarean delivery on the risk of uterine rupture has been studied extensively In a meta-analysis, Mozurkewich andHutton used pooled data from 11 studies and showed that the uterine rupture rate for women undergoing a TOLAC was 0.39% comparedwith 0.16% for patients undergoing elective repeat cesarean delivery (odds ratio [OR], 2.10; 95% CI, 1.45-3.05) After restricting the meta-analysis to 5 prospective cohort trials, similar results were found (OR, 2.06; 95% CI, 1.40-3.04). [26]

Hibbard et al examined the risk of uterine rupture in 1,324 women who underwent a TOLAC They reported a significant difference in therisk of uterine rupture between women who achieved successful vaginal birth compared with women in whom attempted vaginal deliveryfailed (0.22% vs 1.9%; OR, 8.9; 95% CI, 1.9-42). [27] The effect of previous cesarean delivery on the rate of subsequent pregnancy-relateduterine rupture can be further examined according to additional subcategories, which are summarized in Table 1

Relevant to this issue of vaginal birth after cesarean section (VBAC) is that the overall rate in the United States increased from 3.4% in

1980 to a peak of 28% in 1996 Commensurate with this 8-fold increase in the VBAC rate, reports of maternal and perinatal morbidity alsoincreased, in particular with reference to uterine rupture By 2007, the VBAC rate in the United States had fallen nationally to 8.5% Notsurprisingly, the cesarean delivery rate also reached an all-time high of 32% in 2007 In its most recent guidelines pertaining to VBAC inAugust 2010, the American Congress of Obstetricians and Gynecologists (ACOG) adopted the recommendation not to restrict women'saccess to VBAC. [28] This occurred after the National Institutes of Health (NIH) Consensus Development Conference Panel reviewed thetotality of the evidence concerning maternal and neonatal outcomes relating to VBAC in March 2010. [29]

Previous classic cesarean delivery

Classic cesarean delivery via vertical midline uterine incision is infrequently performed in the modern era and currently account for 0.5% ofall births in the United States. [30] In a meta-analysis, Rosen et al reported an 11.5% absolute risk of uterine rupture (3 of 26 cases) inwomen with classic vertical cesarean scars who underwent an unplanned TOLAC. [31] For women who underwent repeat cesarean section,Chauhan et al reported that the uterine rupture rate for 157 women with prior classical uterine cesarean scars was 0.64% (95% CI, 0.1-3.5%) All patients in that study underwent repeat cesarean delivery, but a high rate of preterm labor resulted in 49% of the patients being

in labor at the time of their cesarean delivery. [30]

Landon et al reported a 1.9% absolute uterine rupture rate (2 of 105 cases) in women with a previous classic, inverted T, or J incision who

either presented in advanced labor or refused repeat cesarean delivery. [32] These rates of frank uterine rupture in women with classiccesarean deliveries are in contrast to the higher rates of 4-9% that the American College of Obstetricians and Gynecologists (ACOG) hadhistorically reported for women with these types of uterine scars However, Chauhan et al observed a 9% rate of asymptomatic uterine scardehiscence (95% CI, 5-15%). [30] This result suggests that disruptions of uterine scars might have been misclassified as true rupturesinstead of dehiscences in previous studies; this error may explain the bulk of the discrepancy

Previous low vertical cesarean delivery

A meta-analysis of pooled data from 5 studies demonstrated a 1.1% absolute risk (12 of 1,112 cases) of symptomatic uterine rupture inwomen undergoing a TOLAC with a low vertical cesarean scar. [32, 33, 34, 35, 36] Compared to women with low transverse cesarean scars,these data suggest no significantly increased risk of uterine rupture or adverse maternal and perinatal outcomes

Interpretation of these studies is hampered by inconsistencies in how high the lower uterine segment could be cut before it was considered

a classic incision Even when the lower uterine segment is already well developed as a result of active labor, a low vertical incision ofadequate length is often impossible to permit fetal delivery Naef et al arbitrarily defined a 2-cm extension into the upper segment as aclassic extension For 322 pregnancies that occurred after a low vertical cesarean delivery, the overall rate of uterine rupture was 0.62%.This rate could be further divided as 1.15% for 174 women who underwent a TOLAC compared with no ruptures among 148 women whounderwent elective repeat cesarean delivery. [33]

Unknown uterine scar

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In many instances, the type of incision used for a prior cesarean delivery cannot be confirmed due to unavailability of the operative report.Under these circumstances, the assessment of uterine rupture risk may sometimes be guided by the obstetric history to infer the mostprobable type of uterine scar For example, a patient with a history of a preterm cesarean delivery at 28 weeks’ gestation has a muchhigher likelihood of having had a vertical uterine incision than a patient who underwent a cesarean section for an indication of arrest of fetaldescent at term

It has been argued that because most cesarean deliveries in the United States are accomplished via low-transverse uterine incisions, therisk of uterine rupture for patients with an unknown scar is similar to that for women who have previously undergone a low-transversehysterotomy This logic depends on the high ratio of low-transverse to vertical incisions performed for cesarean section, but it ignores thevarying probability with which different types of uterine incisions are made under different obstetrical circumstances, as well as differencesthat occur due to varying medical resources and the prevailing local practitioner practices in countries other than the United States (eg,practices that occur in other countries, such as Mexico or Brazil) Nevertheless, the vast majority of cesarean deliveries performed in theUnited States are accomplished via low-transverse uterine incisions

In a small case-control study of 70 patients by Leung et al, no association was found between an unknown uterine scar and the risk ofuterine rupture; however, given the rarity of uterine rupture (see Table 1), this study was vastly underpowered to detect such a difference

[37] Two additional, but similarly underpowered, case series have also reported comparable rates of uterine rupture and VBAC success inwomen with unknown uterine cesarean delivery scars versus those with documented previous low-transverse hysterotomies. [38, 39] TheMaternal-Fetal Medicine Units (MFMU) Network cesarean delivery registry reports a 0.5% risk (15 of 3,206) of uterine rupture for patientswho underwent a TOLAC with an unknown uterine scar. [32]

For cases in which there are 1 or 2 unknown prior uterine incisions, there is a single small, randomized, controlled trial by Grubb et al thatcompared labor augmentation with oxytocin (n=95) with no intervention (n=93) in women with prior cesarean deliveries involving either 1 or

2 unknown uterine incisions Four uterine dehiscences and 1 uterine rupture occurred, all in the group that underwent labor augmentation

In the 1 case of uterine rupture, the unknown uterine scar was in a patient with 2 prior cesarean deliveries, one of which involved a verticalincision Had the uterine scar status for this patient been known in advance, it would have represented a contraindication to TOLAC. [40]

Previous low transverse cesarean delivery

The risk of uterine rupture after a low transverse cesarean delivery varies depending on whether patients undergo a TOLAC or an electiverepeat cesarean delivery and on whether labor is induced or spontaneous, as well as other factors The vast majority of cesarean

deliveries in the United States are of the low transverse type For women who have had 1 previous cesarean delivery, examining the

various risk factors for uterine rupture is instructive These absolute risks for uterine rupture are discussed below, as well as in Table 1

Previous cesarean delivery without a subsequent trial of labor

In a study of 20,095 women by Lydon-Rochelle et al, the spontaneous uterine rupture rate among 6,980 women with a single cesareandelivery scar who underwent scheduled repeat cesarean delivery without a TOL was 0.16%. [41] This finding indicates that uteri with

cesarean scars have an intrinsic propensity for rupture that exceeds that of the unscarred organ during pregnancy, which is 0.012% (ORincrease of approximately 12-fold) Therefore, all other uterine rupture rates in women with a previous cesarean delivery should be

referenced to this expected baseline rate

Previous cesarean delivery with subsequent spontaneous labor

A study by Lydon-Rochelle et al showed that the uterine rupture rate among 10,789 women with a single previous cesarean delivery wholabored spontaneously during a subsequent singleton pregnancy was 0.52%. [41] This rate of uterine rupture implies an increased relativerisk (RR) of 3.3 (95% CI, 1.8-6.0) for women who labor spontaneously compared with women who undergo elective repeat cesarean

delivery

In a study by Ravasia et al of 1,544 patients with a previous cesarean delivery who later labored spontaneously, the uterine rupture ratewas 0.45%. [42] Zelop et al found that, among 2,214 women with 1 previous cesarean delivery who labored spontaneously, the uterinerupture rate was 0.72%. [43] The authors of this article performed a meta-analysis of 29,263 pregnancies from 9 studies from 1987-2004and showed that the overall risk of uterine rupture was 0.44% for women who labor spontaneously after a previous cesarean delivery

Previous cesarean delivery with subsequent augmentation of labor

Despite the clinical heterogeneity and different VBAC success rates for women undergoing spontaneous labor rather than either laboraugmentation or induction, very few studies have stratified their data by labor augmentation versus labor induction and the data that doexist are conflicting There is wide variance in the frequency of clinical use of oxytocin as well as in the dose and dosing schedules ofoxytocin that are used As a result, there is a paucity of specific evidence-based clinical guidelines for the use of oxytocin in VBAC trials

In a study by Blanchette et al, the rate of uterine rupture for 288 women who underwent oxytocin augmentation of labor after a previouscesarean delivery was 1.4%, compared with 0.34% for 292 women who underwent a trial of spontaneous labor This finding suggests a 4-fold increased risk of uterine rupture in women who undergo labor augmentation with oxytocin compared with spontaneous labor after aprevious cesarean delivery

In the MFMU Network study, the rate of uterine rupture with oxytocin augmentation was 0.9% (52 of 6,009 cases) versus 0.4% (24 of 6,685cases) without oxytocin use In contrast, a meta-analysis of studies published prior to 1989 found that the use of oxytocin was

unassociated with uterine rupture. [29]

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Zelop et al also found that labor augmentation with oxytocin did not significantly increase the risk for uterine rupture. [42] Pooled data inTable 1 show a trend towards an increased rate of uterine rupture, albeit small, with oxytocin use However, the conclusions to be drawnfrom this are both limited and suspect because, in general, no proper adjustment has been made for the potential (and very likely)

confounding-by-indication that occurs in the observational studies that attempt to compare the rate of uterine rupture for women receivingtreatment with oxytocin versus those who do not (eg, proper propensity score matching has not been performed)

In this regard, assessment of the safety of oxytocin use in VBAC trials must consider both the dosage and the time of exposure Theseissues were addressed by Cahill et al in a nested case-control study of 804 patients within a multicenter, retrospective cohort of 25,005patients with at least 1 prior cesarean delivery who underwent a TOLAC At an intravenous oxytocin dosage range of 6-20 mU/min, a morethan 3-fold increased risk of uterine rupture was associated with oxytocin use (HR [hazard ratio], 3.34, 95% CI 1.01-10.98) At dosagerange of more than 20 mU/min, a nearly 4-fold increased risk of uterine rupture (HR, 3.92; 95% CI, 1.06-14.52) was noted The attributablerisk of uterine rupture associated with oxytocin use was 2.9% and 3.6% for the maximum oxytocin dose ranges of more than 20 mU/minand more than 30 mU/min, respectively

The authors did not find a significant risk association between time (in terms of both duration of oxytocin exposure and duration of labor)and uterine rupture risk.They suggest an upper limit of 20 mU/min of oxytocin for use in VBAC trials and a judicious approach to the useand monitoring of oxytocin for both labor augmentation and induction

The benefit of intrauterine pressure catheter (IUPC) monitoring of uterine contractions in VBAC trials is unclear, with only a single smallcase series failing to detect differences in fetal or maternal morbidity/mortality associated with uterine rupture when an IUPC was usedinstead of external tocodynamometry Nevertheless, many institutions have found the IUPC useful in allowing careful titration of oxytocindosing, especially when maternal habitus poses a limit to the accurate external monitoring of uterine contractions in women undergoing aTOLAC

Previous cesarean delivery with subsequent induction of labor

Emerging data indicate that induction of labor after a prior cesarean delivery appears to be associated with an increased risk of uterinerupture

Zelop et al found that the rate of uterine rupture in 560 women who underwent labor induction after a single previous cesarean delivery

was 2.3% compared with 0.72% for 2,214 women who had labored spontaneously (P =.001). [43]

In a study by Ravasia et al of 575 patients who underwent labor induction, the uterine rupture rate was 1.4% compared with 0.45% for

women who labored spontaneously (P =.004). [42]

Blanchette et al found that the uterine rupture rate after previous cesarean delivery when labor was induced was 4% compared with 0.34%for women who labored spontaneously. [44] This last finding suggests a 12-fold increased risk of uterine rupture for women who undergolabor induction after previous cesarean delivery

Data on mechanical methods of labor induction for cervical ripening are limited but reassuring In a small case series, Bujold et al found nostatistically significant difference among the uterine rupture rates of 1.1% for spontaneous labor, 1.2% for induction by amniotomy with or

without oxytocin, and 1.6% for induction by transcervical Foley catheter (P =0.81). [45]

Conversely, Hoffman et al reported a 3.67-fold increased risk of uterine rupture (95% CI, 1.46-9.23) with Foley catheter use for preinductioncervical ripening Importantly, however, many of these patients received concomitant oxytocin together with application of the transcervicalFoley catheter. [46]

Of particular note is that a recent randomized controlled trial by Pettker et al found that the addition of oxytocin to the use of a transcervicalFoley catheter for labor induction does not shorten the time to delivery and has no effect on either the likelihood of delivery within 24 hours

or the vaginal delivery rate. [47] In light of these findings, induction of labor with a transcervical Foley catheter alone may be a reasonableoption for women undergoing a TOLAC with an unfavorable cervix

In a more recent systematic review that evaluated maternal and neonatal outcomes following induction of labor (4,038 women) and

spontaneous labor (13,374 women) in women who previously underwent cesarean section, Rossi and Prefumo reported a lower incidence

of vaginal delivery with induced labor but higher rates of uterine rupture/dehiscence, repeat cesarean section, and postpartum hemorrhage

[48] Hysterectomy and neonatal outcomes were similar between the groups

Facchinetti et al indicated that women with a previous cesarean delivery being induced for premature rupture of membranes and who have

a favorable Bishop have a higher likelihood of success. [49] Significant indicators for a vaginal delivery included a previous vaginal delivery,not being African, and undergoing induction for premature rupture of membranes Women who underwent a repeat cesarean were morelikely to have large babies (≥ 4 kg) and had a higher likelihood of failing labor induction. [49]

Use of prostaglandins for cervical ripening and induction of labor after previous cesarean delivery

Current ACOG guidelines discourage the use of prostaglandins to induce labor in most women with a previous cesarean delivery Thisrecommendation is based on considerable evidence for an increased risk of uterine rupture associated with prostaglandins Lydon-

Rochelle et al reported a 15.6-fold increased risk for uterine rupture (95% CI, 8.1-30) when prostaglandins were used in gravidas whounderwent a TOLAC In 366 women with scars from a previous cesarean delivery who underwent labor induction with prostaglandins, theuterine rupture rate was 2.45% compared with 0.77% without prostaglandin use. [41]

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Taylor et al identified 3 uterine ruptures among 58 patients with 1 previous cesarean delivery who received prostaglandin E2 (PGE2) alonefor labor induction The uterine rupture rate was 5.2% (3 of 58) compared with 1.1% (8 of 732) among patients not treated with

prostaglandin. [50] Ravasia et al found that 3 ruptures occurred among 172 patients who underwent labor induction with PGE2 alone

(1.7%), which was significantly higher than 0.45% (7 of 1,544) women who labored spontaneously. [42]

In contrast, Flamm et al found a uterine rupture rate of 1.3% (6 of 453) in patients with a previous cesarean delivery who were treated withPGE2 in combination with oxytocin This result was not significantly different from the rate of 0.7% (33 of 4,569) in women who were nottreated with PGE2. [51] In a small study, Delaney and Young also did not find a significant difference in uterine rupture rates between

patients with scars from a previous cesarean delivery who underwent labor induction with PGE2 and patients with previous cesarean scars

who labored spontaneously (1.1 vs 0.3%; P =.15). [52]

Landon et al reported no uterine ruptures among 227 patients who underwent induction with prostaglandins alone Although the study wasunderpowered to detect small differences, the particular type of prostaglandin administered did not appear to significantly affect the uterinerupture rate (52 patients received misoprostol; 111, dinoprostone; 60, PGE2 gel; and 4, combined prostaglandins). [32]

Previous cesarean delivery with previous successful vaginal delivery

Several studies have shown a protective association of previous vaginal birth on uterine rupture risk in subsequent attempts at vaginal birthafter previous cesarean delivery Zelop et al compared 1,021 women who underwent a TOL after a single previous cesarean delivery with 1previous vaginal delivery with 2,762 women who underwent a TOL with no previous vaginal delivery The uterine rupture rate was 0.2%

versus 1.1% (P =.01). [53]

Among women with a single uterine scar, those with at least 1 previous vaginal delivery had one fifth the risk for uterine rupture comparedwith women without a previous vaginal delivery (OR, 0.2; 95% CI, 0.04-0.8) Caughey et al found that women with a previous vaginaldelivery were about one fourth as likely as patients without a previous vaginal delivery to have a uterine rupture (OR, 0.26; 95% CI, 0.08-0.88). [54] In a study of 205 patients who underwent a TOL after 1 previous cesarean delivery, Kayani and Alfirevic noted that all 4 of theircases of uterine ruptures occurred in women with no previous vaginal delivery. [55]

A study of 11,778 women by members of the Maternal-Fetal Medicine Units (MFMU) Network found that in women with no prior vaginaldelivery who underwent a TOLAC, there was an increased risk of uterine rupture with induction versus spontaneous labor (1.5% vs 0.8%,

P =0.02) In contrast, no statistically significant difference was shown for women with a prior vaginal delivery who underwent spontaneous

TOLAC compared with labor induction (0.6% vs 0.4%, P =0.42). [56]

Previous cesarean delivery with subsequent successful VBACs

Multiple studies suggest a protective advantage with regard to the uterine rupture rate if a woman has had a prior successful VBAC

attempt Multiple potential explanations exist, but the 2 most obvious are that a successful prior VBAC attempt assures that (1) the

maternal pelvis is tested and that the bony pelvis is adequate to permit passage of the fetus and (2) the integrity of the uterine scar hasbeen tested previously under the stress/strain conditions during labor and delivery that were adequate to result in vaginal delivery withoutprior uterine rupture

Mercer et al found that the rate of uterine rupture decreased after the first successful VBAC, but that there was no additional protectiveeffect demonstrated thereafter: the uterine rupture rate was 0.87% with no prior VBACs, 0.45% for those with one successful prior VBAC,

and 0.43% for those with 2 or more successful prior VBACs (P =.01). [57] Pooled data from 5 studies indicate an increased uterine rupturerate of 1.4% (1 per 73) in failed VBAC attempts that required a repeat cesarean section in labor. [32, 44, 58, 59, 60]

Interdelivery interval

In a case-control study by Esposito et al, an interpregnancy interval between cesarean delivery and a subsequent pregnancy of < 6 monthswas nearly 4 times as common among patients who had uterine rupture than in control subjects (17.4 vs 4.7%; OR, 3.92; 95% CI, 1.09-14.3) Among 23 patients who had uterine rupture after a previous cesarean delivery, the mean interpregnancy interval was 20.4 ± 15.4

months compared with 36.5 ± 30.4 months for control patients (P =.01). [61] Stamilio et al recently confirmed a similar uterine rupture rate of2.7% in women with an interdelivery interval of < 6 months compared with 0.9% for those having interdelivery intervals of ≥6 months

(adjusted OR 2.66, 95% CI, 1.21-5.82). [62]

Shipp et al similarly found that the risk of symptomatic uterine rupture was increased 3-fold in women with interdelivery intervals of< 18months when they underwent a TOLAC after 1 previous cesarean delivery (OR, 3.0; 95% CI, 1.2-7.2). [63] The authors controlled for

maternal age, public assistance, length of labor, gestational age of ³41 weeks, and induction of augmentation of labor with oxytocin

In additional support of this observation, a Canadian study by Bujold et al reported on 1,527 women who underwent a TOL after a singleprevious low-transverse cesarean delivery, finding that 2.8% of patients who had an interdelivery interval of ≤24 months had a uterine

rupture compared with 0.9% for those with an interdelivery interval of >24 months (P < 01). [64] After adjusting for confounding variables,the odds ratio for a uterine rupture during a subsequent TOLAC was 2.65 for women who had an interdelivery interval of ≤24 monthscompared with women who had a longer interdelivery interval (95% CI, 1.08-5.46)

In a follow-up study, the same authors examined the risk of uterine rupture between 18-24 months After adjustment for confounding

factors, they found that an interdelivery interval shorter than 18 months was associated with a significant increase of uterine rupture (oddsratio [OR], 3; 95% confidence interval [CI], 1.3–7.2), whereas an interdelivery interval of 18-24 months was not (OR, 1.1; 95% CI, 0.4–3.2)

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In agreement with the findings by Shipp et al, the study by Bujold et al concludes that an interdelivery interval shorter than 18 months butnot between 18-24 months should be considered as a risk factor for uterine rupture. [65]

The authors speculated that a prolonged interpregnancy interval may allow time for the previous cesarean delivery scar to reach its

maximal tensile strength before the scar undergoes the mechanical stress and strain with a subsequent intrauterine pregnancy

Interestingly, the authors also observed that the combination of a short interdelivery interval of ≤24 months and a single-layer hysterotomyclosure was associated with a uterine rupture rate of 5.6% This is comparable to the rate of uterine rupture for patients undergoing aTOLAC with a previous classic midline cesarean scar

One-layer versus 2-layer hysterotomy closure

In a Canadian study of 1,980 women who underwent a TOL after a single previous low transverse cesarean delivery, Bujold et al found a

4-to 5-fold increased risk of uterine rupture for women who had a previous single-layer uterine closure compared with those having a layer closure Uterine rupture occurred in 3.1% (15 of 489 cases) of single-layer closure versus 0.5% (8 of 1,491 cases) of two-layer

two-closure (P < 001) Using stepwise multivariate logistic regression, the authors concluded that the OR for uterine rupture in women who

had undergone a single previous one-layer cesarean hysterotomy closure was 3.95 (95% CI, 1.35-11.49) compared with those who had atwo-layer closure. [66]

The same authors reported a multicenter, case-control study comparing 96 cases of uterine rupture with 288 controls Prior single-layerclosure carried more than twice the risk of uterine rupture compared with two-layer closure In multivariate analysis, single-layer closurewas linked to an increased rate of uterine rupture (odds ratio [OR] 2.69; 95% confidence interval [CI] 1.37–5.28) The authors concludedthat single-layer closure should be avoided in women who contemplate future VBAC delivery. [67]

Durnwald and Mercer found that 182 patients with single-layer hysterotomy closure did not have an increased rate of uterine rupture, but

the rate of uterine windows at subsequent delivery was increased to 3.5% versus 0.7% for those who had a multi-layer closure (P =.046).

[68]

Gyamfi et al reported an 8.6% (3 of 35) rate of uterine rupture in patients with a single-layer closure compared with 1.3% (12 of 913) in

those with double-layer closure (P =0.015) Although the single-layer group had a shorter interdelivery interval, the uterine rupture rate remained significantly elevated even when the time interval was controlled for using logistic regression (OR 7.20, 95% CI, 1.81-28.62, P

=0.005). [69]

Multiple prior cesarean deliveries

For women with a history of 2 or more cesarean deliveries, 10 studies published from 1993-2010 showed that the risk of uterine rupture in

a subsequent pregnancy ranged from 0.9-6.0% (1 per 17-108 pregnancies) This risk is increased 2- to 16-fold compared to women withonly a single previous cesarean delivery In a study of 17,322 women with scars from cesarean delivery, Miller et al found that, when

women underwent a TOLAC, uterine rupture was 3 times more common with 2 or more scars (1.7%) than with 1 scar (0.6%) [OR, 3.06;

95% CI, 1.95-4.79; P < 001]. [70]

In the largest analysis to date, Macones et al reviewed data from 17 tertiary and community hospitals and found that, in 1,082 women with

2 uterine scars who underwent a TOLAC, the risk of uterine rupture was increased 2-fold compared with women with only 1 uterine scar(absolute rupture risk 1.8% vs 0.9%; adjusted OR, 2.3; 95% CI, 1.37-3.85). [71]

In the only study to control for potential confounding variables, Caughey et al concluded that in women who had 2 previous cesareandeliveries who then attempted vaginal birth, the risk of uterine rupture was almost 5 times the risk of those with only 1 previous cesarean

delivery (3.7% vs 0.8%; P =.001) The study controlled for several key covariates, including the use of prostaglandin E2 gel, oxytocin

induction, oxytocin augmentation, length of labor, and epidural use They also found that women with a previous vaginal delivery wereabout one fourth as likely to have a uterine rupture as women without a previous vaginal delivery (OR, 0.26; 95% CI, 0.08-0.88). [54]

In contrast, Landon et al reported through the MFMU Network that there was no significant difference in the uterine rupture rate for women

with multiple prior cesarean deliveries versus 1 prior cesarean delivery (0.9% vs 0.7%; P= 0.37). [72] However, in this study there was amuch lower TOLAC rate of 9% for women with multiple prior cesarean deliveries compared with the 27% rate in the report of Macones et al

[71] and the 73% rate in Miller’s study. [70] This indicates that there were much more stringent inclusion/exclusion criteria applied by Landon

et al, and that this difference may account for the apparent discrepancy in outcomes Caughey et al did not report the TOLAC rate in their12-year data analysis. [54]

A recent meta-analysis of 17 studies including 5,666 patients undergoing a TOL after 2 or more cesarean deliveries demonstrated a 1.36%uterine rupture rate. [73] This is similar to the result of our pooled data analysis from 10 studies published from 1993-2010, which shows a1.81% uterine rupture rate for patients with multiple previous cesarean delivery scars

A 2004 ACOG guideline suggested that in women with 2 previous cesarean deliveries, only those with a previous vaginal delivery should

be considered candidates for a TOLAC. [74] This ACOG recommendation was subsequently revised in an updated 2010 guideline to

suggest that women with two previous low transverse cesarean deliveries may be considered candidates for TOLAC regardless of theirprior vaginal delivery status. [28]

Maternal age

Shipp et al showed that advancing maternal age is associated with an increased rate of uterine rupture In a multiple logistic regressionanalysis designed to control for confounding factors, the overall rate of uterine rupture among 3,015 women with 1 previous cesarean

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Similarly, Cahill et al compared 535 twin pregnancies with 24,307 singleton pregnancies and reported a comparable uterine rupture rate of1.1% for twin vs 0.9% for singleton pregnancies (OR, 1.2; 95% CI, 0.3-4.6) in women with at least 1 previous cesarean delivery undergoingTOLAC. [77] Additionally, they found that patients with twins were less likely to attempt a TOLAC (OR, 0.3; 95% CI 0.2-.04), but no morelikely to have a VBAC failure (OR, 1.1; 95% CI, 0.8-1.6), or major maternal morbidity (OR, 1.6; 95% CI, 0.7-3.7)

Overall, women with multifetal gestations attempting VBAC did not incur any greater risk of uterine rupture than their singleton controls In

a nested case-control study of the MFMU cesarean registry, Varner et al compared cases of women undergoing TOLAC with one previouscesarean delivery with a multifetal pregnancy versus controls with one previous cesarean delivery with a singleton pregnancy. [78] A similaruterine rupture rate of 0.7% was found in both multifetal (4/556) versus singleton groups (99/13,923) [ORadj 1.19 (0.43-3.30)] In a smallerstudy, Aaronson et al reported no cases of uterine rupture among 134 twin pregnancies undergoing a TOLAC with a single prior cesareansection. [79] The ACOG 2010 guidelines for VBAC recommend that women with one previous cesarean delivery with a low transverseincision, who are otherwise appropriate candidates for twin vaginal delivery, may be considered candidates for TOLAC. [28]

Fetal macrosomia

Elkousy et al found that, in 9,960 women who underwent a TOLAC after 1 previous cesarean delivery, the risk of uterine rupture was

significantly greater for fetuses that weighed more than 4000 g (2.8%) than in those weighing less than 4000 g (1.2%; RR 2.3, P < 001).

For women with 1 previous cesarean delivery and no previous vaginal deliveries, the uterine rupture rate was 3.6% for women with a fetal

weight of more than 4000 g compared to women with a fetal weight of < 4000 g (RR 2.3, P < 001). [80] More recently, Jastrow et al showedthat birth weight was directly correlated with the rate of uterine rupture, with uterine rupture rates of 0.9%, 1.8%, and 2.6% for birth weights

of less than 3500 g, 3500-3999 g, and 4000 g or larger, respectively (P < 05). [81]

Zelop et al reported that the rate of uterine rupture for women delivering neonates weighing >4000 g was 1.6% versus 1% for newborns

≤4000 g, but that the difference was not statistically significant (P =0.24). [82] Flamm et al examined TOLAC risks in a cohort of 301 womenand reported no difference between the rates of uterine rupture for women with neonates weighing ≥4000 gm versus < 4000 gm. [83] TheACOG 2010 VBAC guidelines suggest that suspected fetal macrosomia alone should not preclude the possibility of TOLAC. [28]

Gestation beyond 40 weeks

The effect of advancing gestational age on the safety and success of TOLAC is of great clinical significance in the counseling of posttermVBAC candidates In a Canadian study that evaluated 329 patients with advanced gestational age of ≥41 weeks, Hammoud et al reported

a significantly increased rate of uterine rupture of 2.7% compared to 1.0% among 1,911 patients with gestational ages between 37-40 6/7weeks (p=0.006). [84] After adjusting for confounding variables, advanced gestational age was associated with a lower rate of successfulvaginal delivery (OR 0.68, 95% CI 0.51–0.89) and a higher rate of uterine rupture (OR 2.85, 95% CI 1.27–6.42) when compared to thosepregnancies of gestational age between 37–40 6/7 weeks Similarly, a British study by Kiran et al found a significantly increased rate ofuterine rupture of 2.1% (10 of 466) in women undergoing TOLAC beyond 40 weeks of gestation compared to 0.3% (4 of 1,154)

forthosewithgestationalagesof≤40weeks(OR6.3,CI1.9-20.2). [85]

The largest study to evaluate the effect of delivery beyond 40 weeks of gestation has not found this association, however Among 4,680women undergoing a TOLAC at a gestational age of 40 weeks or longer, Coassolo et al reported a uterine rupture rate of 1.1% (52 of4,680), which was not statistically different from the uterine rupture rate of 1.0% (68 of 6,907) found in women with a gestational age of lessthan 40 weeks. [86] When the investigational cohort was defined as those pregnancies of 41 weeks' gestation or longer, the risk of uterinerupture and overall morbidity was also not increased

The difference in these results may arise from the small sample sizes of the Canadian and British studies and/or the accuracy of

gestational age estimates by last menstrual period dating with early ultrasound confirmation, which was not clearly defined in the study ofCoassalo et al Zelop et al reported similar findings of no significant difference in uterine rupture rate of 1.3% (17 of 1,271) in women

undergoing TOLAC at more than 40 weeks of gestation versus 0.8% (12 of 1,504) in women at 37-40 weeks of gestation (P = 0.2). [87]

Moreover, the latter authors reported that the risk of uterine rupture does not increase substantially after 40 weeks of gestation, but isincreased with induction of labor regardless of gestational age For spontaneous labor, uterine ruptures occurred in 0.5% of gravidas

delivering at or before 40 weeks compared with 1.0% for those delivering after 40 weeks (P = 0.2) For induced labor, the rates of uterinerupture were 2.1% for gravidas at or before 40 weeks and 2.6% for those after 40 weeks (P = 0.7)

The ACOG 2010 VBAC guidelines suggest that although the chance of success may be lower for a vaginal delivery in more advancedgestations, gestational age beyond 40 weeks alone should not preclude a TOLAC. [28] [#Table1]

Table 1 Absolute Rates of Uterine Rupture for Different Patient Subgroups (Open Table in a new window)

General Subcategory Uterine Years No References

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of DataCollection ofStudies

Major Minor TotalDeliveries Rate

Total

No

in category

2003, Yap2001,Leung

1993, Miller1997,Kieser2002,Bujold

2002, Ofir2004,Flamm1994,Menihan

1998, Zwart2009

Unscarred

uterus

Inindustrializedcountries NA 1,467,534

1 per8,434(0.013%) 174

Gardeil1994,Plauche1984,Gregory1999,Rageth

1999, Yap

2001, Miller1997,Kieser2002,Zwart, 2009

In developing NA 399,314 1 per 920 434 1966-2006 4 Golan, 1980,

9/9/2017 Uterine Rupture in Pregnancy: Overview, Rupture of the Unscarred Uterus, Previous Uterine Myomectomy and Uterine Rupture

1976,Rahman

1985, Gupta2010Elective

Gregory1999

NA 190 1 per 95(1.1%) 2 1992-2002 2 Ravasia1999, Erez

2008, Sizzi2007,Makino2008Trans-

abdominal

1 per 60(1.7%) 3 1930-1960 2 Brown 1956,Garnet 1964

Laparoscopic

myomectomy NA 822 1 per206(0.49%) 4 1989-2006 8

Dubuisson2000,Seinera2000,Nezhat,1999,Seracchioli2000,Seracchioli2006,Kumakiri

2008, Sizzi2007,Makino 2008Normal

uterus,

previous

236(0.42%)

1983-2002 13 Gardeil1994,

Landon

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cesarean

Lydon-Rochelle2001,Blanchette2001,Grobman2007,Rageth

1999, Miller

1994, Yap2001,Leung1993,Kieser2002,Flamm1994,Cowan

1994, Lin2004

Elective repeat

cesarean

1 per 623(0.16%) 145 1982-2002 10

Gardeil1994,Mozurkewich2000,Landon

2004, Rochelle2001,Blanchette2001,Gregory1999,McMahon1996,Rageth

Lydon-1999, Kieser

2002, Lin2004

(0.58%) 970 1982-2002 22 Gardeil1994,

Mozurkewich2000,Hibbard2001,Landon

2004, Rochelle2001,Ravasia

Lydon-2000, Zelop1999,Blanchette

2001, Taylor2002,Grobman2007,Gregory1999,McMahon1996,Rageth

1999, Leung

1993, Kieser

2002, Flamm1994,Menihan1998,Phelan1987,