Obstetrics & Gynecology:
Risk of Uterine Rupture and Placenta Accreta With Prior Uterine Surgery Outside of the Lower Segment
Gyamfi-Bannerman, Cynthia MD; Gilbert, Sharon MS, MBA; Landon, Mark B. MD; Spong, Catherine Y. MD; Rouse, Dwight J. MD; Varner, Michael W. MD; Caritis, Steve N. MD; Meis, Paul J. MD; Wapner, Ronald J. MD; Sorokin, Yoram MD; Carpenter, Marshall MD; Peaceman, Alan M. MD; O'Sullivan, Mary J. MD; Sibai, Baha M. MD; Thorp, John M. MD; Ramin, Susan M. MD; Mercer, Brian M. MD; for the Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD) Maternal-Fetal Medicine Units (MFMU) Network
Departments of Obstetrics and Gynecology, Columbia University, New York, New York, Ohio State University, Columbus, Ohio, University of Alabama at Birmingham, Birmingham, Alabama, University of Utah, Salt Lake City, Utah, University of Pittsburgh, Pittsburgh, Pennsylvania, Wake Forest University Health Sciences, Winston-Salem, North Carolina, Thomas Jefferson University, Philadelphia, Pennsylvania, Wayne State University, Detroit, Michigan, Brown University, Providence, Rhode Island, Northwestern University, Chicago, Illinois, University of Miami, Miami, Florida, University of Tennessee, Memphis, Tennessee, University of North Carolina, Chapel Hill, North Carolina, University of Texas Health Science Center at Houston, Houston, Texas, and Case Western Reserve University-MetroHealth Medical Center, Cleveland, Ohio; The George Washington University Biostatistics Center, Washington, DC; and the Eunice Kennedy Shriver National Institute of Child Health and Human Development, Bethesda, Maryland.
Corresponding author: Cynthia Gyamfi-Bannerman, MD, Associate Clinical Professor, Columbia University Medical Center, Department of Obstetrics and Gynecology, Division of Maternal-Fetal Medicine, 622 West 168th Street, PH-16, New York, NY 10032; e-mail: firstname.lastname@example.org.
The project described was supported by grants from the Eunice Kennedy Shriver National Institute of Child Health and Human Development of the National Institutes of Health (grants HD21410, HD21414, HD27860, HD27861, HD27869, HD27905, HD27915, HD27917, HD34116, HD34122, HD34136, HD34208, HD34210, HD40500, HD40485, HD40544, HD40545, HD40560, HD40512, and HD36801), and its contents are solely the responsibility of the authors and do not necessarily represent the official view of Eunice Kennedy Shriver National Institute of Child Health and Human Development or the National Institutes of Health.
Financial Disclosure The authors did not report any potential conflicts of interest.
Presented at the Society for Gynecologic Investigation, March 24--27, 2010, Orlando, Florida.
* For a list of other members of the NICHD MFMU, see the Appendix online at http://links.lww.com/AOG/A331.
The authors thank Francee Johnson, RN, BSN, for protocol development and coordination between clinical research centers; Elizabeth Thom, PhD, for protocol and data management and statistical analysis; and Ronald J. Wapner, MD, and John C. Hauth, MD, for protocol development and oversight.
Dr. Spong, Associate Editor of Obstetrics & Gynecology, was not involved in the review of this article or the decision to publish this article.
OBJECTIVE: Women with a prior myomectomy or prior classical cesarean delivery often have early delivery by cesarean because of concern for uterine rupture. Although theoretically at increased risk for placenta accreta, this risk has not been well-quantified. Our objective was to estimate and compare the risks of uterine rupture and placenta accreta in women with prior uterine surgery.
METHODS: Women with prior myomectomy or prior classical cesarean delivery were compared with women with a prior low-segment transverse cesarean delivery to estimate rates of both uterine rupture and placenta accreta.
RESULTS: One hundred seventy-six women with a prior myomectomy, 455 with a prior classical cesarean delivery, and 13,273 women with a prior low-segment transverse cesarean delivery were evaluated. Mean gestational age at delivery differed by group (P<.001), prior myomectomy (37.3 weeks), prior classical cesarean delivery (35.8 weeks), and low-segment transverse cesarean delivery (38.6 weeks). The frequency of uterine rupture in the prior myomectomy group (P-MMX group) was 0% (95% confidence interval [CI] 0–1.98%). The frequency of uterine rupture in the low-segment transverse cesarean delivery group (LTC group) (0.41%) was not statistically different from the risk in the P-MMX group (P>.99) or in the prior classical cesarean delivery group (PC group) (0.88%; P=.13). Placenta accreta occurred in 0% (95% CI 0–1.98%) of the P-MMX group compared with 0.19% in the LTC group (P>.99) and 0.88% in the PC group (P=.01 relative to the LTC group). The adjusted odds ratio for the PC group (relative to LTC group) was 3.23 (95% CI 1.11–9.39) for uterine rupture and 2.09 (95% CI 0.69–6.33) for accreta. The frequency of accreta for those with previa was 11.1% for the PC group and 13.6% for the LTC group (P>.99).
CONCLUSION: A prior myomectomy is not associated with higher risks of either uterine rupture or placenta accreta. The absolute risks of uterine rupture and accreta after prior myomectomy are low.
The theoretical risk of uterine rupture before the onset of labor in women with a prior classical cesarean delivery has led some practitioners to move the gestational age at delivery for these women into the late preterm period (34 0/7 to 36 6/7 weeks).1,2 Delivery for women with prior myomectomies has followed this trend because it is thought that the scar from a myomectomy is functionally equivalent to the scar from a classical cesarean delivery.1,2 In practice, there is a paucity of data on uterine rupture risk in women with a prior myomectomy.3–5 Similarly, there are little data available about the rates of placenta accreta in women with prior uterine scars other than low-segment transverse. Thus, our primary aim was to describe the risks of uterine rupture in women with a prior myomectomy, prior classical cesarean delivery, and prior lower-segment cesarean delivery, and our secondary aim was to compare risks of placenta accreta in these populations.
MATERIALS AND METHODS
This is a secondary analysis of the Cesarean Registry, a multicenter observational study of women undergoing both primary and repeat cesarean delivery as well as those attempting trial of labor after prior cesarean delivery. The study was conducted by the Eunice Kennedy Shriver National Institute of Child Health and Human Development Maternal-Fetal Medicine Units Network from 1999 to 2000 at 19 U.S. academic centers. Full details of the methods and study design have been described previously.6 This secondary analysis was approved by the Institutional Review Board at Columbia University Medical Center.
In the parent study, women delivered either vaginally or by cesarean. Uterine rupture was defined as a through-and-through disruption or tear of the uterine muscle and serosa; fetal contents may or may not have extruded into the abdomen. Placenta accreta was defined as a placenta that was adherent to the uterine wall without easy separation. In cases in which a pathology report was available, it took precedence over the clinical findings. The definition of placenta previa was based on the presence of a clinician diagnosis of previa with or without bleeding after taking into consideration the clinical presentation and imaging results.
For this specific analysis, women with a singleton gestation and a prior myomectomy, as reported by the patient and documented in the chart, or one prior cesarean delivery were included. Our sample size was fixed by available patients meeting inclusion criteria from the parent study. We excluded patients with both a prior myomectomy and a prior cesarean delivery. Additionally, women with a prior T or J uterine incision were excluded. The women with a prior cesarean delivery were divided into two groups by type of scar: prior classical cesarean delivery (PC group) and prior low-segment transverse cesarean (LTC group). These women were compared with the prior myomectomy group (P-MMX group) to evaluate rates of both uterine rupture and placenta accreta. Type of prior scar was abstracted from the medical record supplemented by direct review of the operative reports when available.
We chose women with one prior low-segment transverse cesarean delivery as the reference group for the primary outcome. We compared uterine rupture in the LTC group with women in the P-MMX group and PC group. Similarly, the LTC group was used as a reference for the secondary outcome, placenta accreta. Because it is known that placenta previa modifies the risk of placenta accreta, our final analysis evaluated rates of accreta in the three groups when a previa was present.
For statistical analyses, categorical variables were compared using the χ2 test or Fisher exact test for dichotomous variables and the Kruskall-Wallace test for continuous variables. For one-sample binomial interval estimation, the Blyth-Still-Casella interval was used, an exact confidence interval (CI) that is considered more conservative or shorter in width than the commonly used Clopper-Pearson CIs.7 Pair-wise comparisons were performed using Tukey Honestly Significant Difference test. Multivariable logistic regression was used to adjust results for uterine rupture by potential confounders. These confounders included gestational age at delivery, which was determined by the best obstetric measurement assigned by the local caregivers, induction of labor defined as the administration of a drug such as oxytocin to initiate labor, and maternal age at delivery. Odds ratios and 95% CIs for outcomes were determined. Nominal two-sided probability values are reported with statistical significance defined as P<.05 without adjustments for multiple comparisons. Statistical analyses were performed using SAS (SAS Institute Inc, Cary, NC) and StatXact (Cytel Software, Cambridge, MA).
Out of 47,112 women in the Cesarean Registry, we identified 176 women who had a prior myomectomy, 13,273 with one prior low-segment transverse cesarean delivery, and 455 who had a prior classical cesarean delivery who met the inclusion criteria for our study (N=13,904). Details regarding the excluded patients are shown in Figure 1. Of the final cohort, all patients in the P-MMX group delivered by cesarean, whereas 27 (5.9%) in the PC group and 5,873 (44.2%) in the LTC group delivered vaginally. Demographic and labor characteristics of our cohort differed between groups (Table 1). Women with prior myomectomy or prior classical cesarean delivery were significantly more likely to be African American, whereas those with a prior low-segment transverse cesarean delivery were more likely to be Caucasian (P<.001). Women in the P-MMX group were older compared with the other groups (Tukey pair-wise comparison, all P<.05). Finally, women with a prior low-segment transverse cesarean had the highest mean gestational age at delivery and were the most likely to have labored (all P<.001).
The main outcome results are presented in Table 2. The frequency of uterine rupture risk in the P-MMX group (0%, 95% CI 0–1.98%) was not significantly different from the risk in the LTC group (0.41%, 95% CI 0.31–0.53%; P>.99). The frequency of rupture in the PC group (0.88%, 95% CI 0.30–2.19%) also was not significantly different when compared with the LTC group, (P=.13). However, after controlling for factors (maternal age, gestational age at delivery, and induction) that may influence the rate of rupture, we found that only the PC group had a higher risk of uterine rupture (odds ratio 3.23, 95% CI 1.11–9.39) compared with the LTC group (Table 3). Additionally, although the PC group was delivered earlier than those in the P-MMX group (mean 35.8 compared with 37.3 weeks), the frequency of uterine rupture in the two groups (0.88% compared with 0%) was not significantly different (P=.58). Twenty-one percent of women with prior myomectomy, 36.7% of women with prior classical cesarean delivery, and 66.5% of women with low-segment transverse cesarean delivery had signs of labor (ie, regular contractions); the respective uterine rupture frequencies with labor were 0%, 1.8%, and 0.6% (P=.14). Also, 1.1% with prior myomectomy, 2.6% with prior classical cesarean delivery, and 17.8% with low-segment transverse cesarean delivery had labor induction with respective rupture frequencies of 0%, 0%, and 1.0% (P>.99).
Results for placenta previa and placenta accreta by study groups also are presented in Table 2. The frequency of placenta previa in the LTC group (0.78%) was not different from the risk in the P-MMX group (0.57%; P>.99), but it was significantly lower than the risk in the PC group (1.98%; P=.01). However, after adjusting for potential confounders, this association between prior cesarean delivery and placenta previa disappeared. Additionally, the risks of previa in the P-MMX group and the PC group were not significantly different (P=.30). The unadjusted overall risks of placenta accreta for the groups mirrored the relationship observed for placenta previa, including no statistical difference in the risks of prior myomectomy and prior classical cesarean delivery (P=.58). Also placenta accreta with previa occurred in 0% of the P-MMX group compared with 0.11% in the LTC group (P>.99). Accreta with previa was not different with prior classical cesarean delivery (0.22%) compared with low-segment transverse cesarean delivery (0.11; P=.40). However, among those with previa, the frequencies of accreta were 0%, 11.1%, and 13.6% for the P-MMX, PC delivery, and LTC groups, respectively, although these were not statistically different from each other (all P>.99).
We found that women in the P-MMX group had risks of uterine rupture and accreta comparable with risks in women with a prior low-segment transverse cesarean delivery or a prior cesarean delivery. However, in the PC group, a higher adjusted risk of uterine rupture was observed compared with the LTC group. Consistent with prior studies,8,9 women with low-segment transverse cesarean delivery and a previa had the highest risk of placenta accreta, although we did not demonstrate a statistical difference vis-à-vis the other groups. The absolute risks of placenta accreta overall were low (less than 1%) in all three groups.
There are a number of strengths to our study. As mentioned previously, this is one of the few studies to assess risks of uterine rupture and accreta in a relatively high number of women with a prior uterine surgery outside of the lower segment. The Maternal-Fetal Medicine Units Cesarean Registry provides a comprehensive database of women with a prior cesarean uterine incision who are undergoing a subsequent pregnancy for comparison. However, we acknowledge several study limitations. We did not have access to all operative reports, particularly for the prior myomectomies, so we were not able to ascertain the location of the myomas (eg, subserosal, intramural, or submucosal), whether the endometrial cavities were entered, the extent of the prior surgeries (including number of myomas removed), or type of surgery (laparoscopy compared with laparotomy). Only women with a prior myomectomy who underwent a cesarean delivery are included; any women with a prior myomectomy who delivered vaginally were not captured (although these are likely to be few and unlikely to materially affect our results). Also, only a negligible proportion of the included population had labor or induction; therefore, our sample size is limited to address the risks of a trial of labor after prior myomectomy. Although we cannot comment on whether uterine rupture would have occurred if the pregnancies had continued, despite a 20.5% rate of labor, there remained no ruptures in the P-MMX group.
Few, if any, studies have examined the risks of uterine rupture or accreta in women with a prior myomectomy or classical cesarean delivery. Many clinicians believe that the risk of uterine rupture in women with a prior myomectomy is higher if the endometrial cavity was entered at the time of the myomectomy, and that the risk overall is similar to that seen with prior classical cesarean deliveries. However, there is a paucity of data to support this belief. Still, because of this assertion, women with a prior myomectomy are often delivered by cesarean to prevent the risk of uterine rupture, as evidenced by the relatively comparably low prevalence of labor or labor induction in our series vis-à-vis the LTC group. Furthermore, women with a prior myomectomy are often delivered before 39 weeks (as demonstrated by our data), and often before 37 weeks, to prevent uterine rupture. A review of 412 women with a pregnancy after 1,225 myomectomies at a teaching institution in Nigeria found that the incidence of uterine rupture was low—0.24%.4 Twenty-four of 67 women whose myomectomy dissection involved the endometrial cavity were allowed to labor. None experienced a uterine rupture, but the authors do not state how many went on to deliver vaginally. Similarly, there was a low rate of uterine rupture in our study. There are several case reports of second trimester uterine rupture for patients with a prior classical cesarean scar that have led to these concerns.10,11 Late preterm delivery of women with a prior myomectomy has become a common practice, even though we observed no uterine rupture in the 176 women in our cohort.
In our cohort, the uterine rupture rate in women with a prior classical cesarean delivery was 0.88%. This is in contrast to the rate of uterine rupture that has been quoted as 5–9% in women with a prior classical cesarean who labor.12 This is most likely related to efforts by practitioners to deliver these patients earlier and without labor or labor induction. However, this rate remained significantly high compared with women with a prior low-segment transverse cesarean delivery.
Placenta accreta occurs when the Nitabuch layer is incompletely formed between the placenta and the myometrial layer. It is thought that a scarred uterus is less likely to have an intact Nitabuch layer, increasing the risk for placenta accreta. This is corroborated by the finding that an increasing number of prior cesarean deliveries lead to an increase in the rate of accreta.6,9 Therefore, we sought to estimate whether the risks of accreta were also increased in women with a prior myomectomy or prior classical cesarean delivery. We found uniformly low rates of placenta accreta in these women, although women in the PC group but not the P-MMX group may have a higher risk of accreta than the LTC group (albeit not statistically significant after multivariable adjustment). This supports the findings by Warshak et al3 in their evaluation of the rates of accreta in 453 women with placenta previa, a low-lying placenta, prior cesarean delivery, or prior myomectomy. They found only one case of accreta in women with a prior myomectomy (1 of 39, 2.5%). This finding may be explained by the potentially larger area of disruption from a classical scar as opposed to the smaller myomectomy scar. Despite the lack of pathologic confirmation of accreta, our findings are reassuring for women who have had either a prior myomectomy or a prior classical cesarean delivery because rates of both uterine rupture and placenta accreta are low in our cohort.
In conclusion, the rates of both uterine rupture and placenta accreta are low in women with a prior myomectomy in our cohort. The low risks likely reflect practice patterns that include measures to prevent uterine rupture and other complications. However, considering there is little objective supporting evidence for an optimal delivery gestation age, and considering the morbidity associated with late preterm birth, we would advocate against delivery before 37 completed weeks. Women considering pregnancy after a prior myomectomy can be counseled with these data.
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