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ORIGINAL RESEARCH |
From the Department of Obstetrics and Gynecology, Division of Maternal-Fetal Medicine, University of California, Irvine, California; and Department of Obstetrics and Gynecology, Long Beach Memorial Medical Center, Long Beach, California.
Address reprint requests to: Wilson H. Huang, MD, Las Vegas Perinatal Associates, 400 Shadow Lane, Suite 206, Las Vegas, NV 89106. E-mail: wakamanmd{at}aol.com.
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ABSTRACT |
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METHODS: A retrospective cohort study from January 1, 1997, to December 31, 2000, was conducted. Patients with previous cesarean delivery who attempted VBAC were identified. The analysis was limited to patients at term with one prior cesarean. The interdelivery interval was calculated in months between the index pregnancy and prior cesarean delivery.
RESULTS: A total of 1516 subjects who attempted VBAC were identified among 24,162 deliveries, with complete data available in 1185 cases. The VBAC success rate was 79.0% for patients with an interdelivery interval less than 19 months compared with 85.5% for patients with an interval delivery greater than or equal to 19 months (P = .12). For patients whose labors were induced, interdelivery intervals of less than 19 months were associated with a decreased rate of VBAC success when compared with longer intervals (P < .01). Sufficient power (ß = .95) existed to detect a 64% difference between the groups (
= .05). No significant difference was detected in women who underwent spontaneous labor (P = .98). There was no difference in the rate of symptomatic uterine rupture (P = 1.00).
CONCLUSION: Interdelivery intervals of less than 19 months were associated with a decreased rate of VBAC success in patients who underwent induction, a difference not found in those with spontaneous labor.
The safety of vaginal birth after cesarean (VBAC) has been demonstrated in many studies, and it has been accepted as a way to lower the overall cesarean delivery rate.1 Although there is strong consensus that a trial of labor is appropriate for most women with prior low-transverse cesarean sections, increased experience with VBAC indicates that there are potential problems. Reports have implicated numerous maternal and neonatal complications associated with an unsuccessful trial of labor.2,3
There is little information about the healing of the lower uterine segment cesarean scar. It appears that healing occurs mainly by fibroblast proliferation, and as the scar shrinks, connective tissue proliferation becomes less obvious.4,5 It is plausible that a short interval between deliveries may not allow complete healing of the uterine scar, causing ineffective uterine contractility, poor lower uterine segment thinning, and cervical effacement in labor, or increased potential risk of uterine dehiscence or rupture.
The objective of this study was to determine whether a short interdelivery interval between prior cesarean delivery and trial of labor of the index pregnancy is associated with an increase in maternal and perinatal morbidity and a decrease in the rate of success of VBAC.
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MATERIALS AND METHODS |
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The differences between the groups were analyzed. 
2 and Fisher exact tests were used for categoric variables, and the Student t test was used for continuous variables. A P value of < .05 was considered significant. Multivariate logistic regression analysis was used to evaluate the association of VBAC success with interdelivery interval and other potential confounding factors. Statistical analysis was accomplished using SPSS 8.0 (SPSS Inc., Chicago, IL).
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RESULTS |
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. The VBAC success rate was 79.0% (64 of 81) for patients with interdelivery interval less than 19 months compared with 85.5% (943 of 1104) for patients with interdelivery interval greater than or equal to 19 months (P = .12). Power existed to detect a 12% difference between the groups ( = .05, ß = .80).
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= .05]). We did not find a difference in the rate of VBAC success among patients with no prior vaginal deliveries (70.4% [38 of 54] versus 77.5% [386 of 498]; P = .24). Our multivariate logistic regression analysis found no association between VBAC success, interdelivery intervals, and other potential confounding factors. These include: maternal race; gestational age at delivery; gravidity or parity; history of spontaneous or elective abortions; obstetric service (private versus resident); usage, duration, or dosage of pitocin; indication of cesarean section for prior or index pregnancy; ruptured amniotic membrane; epidural use; evidence of intrapartum chorioamnionitis; meconium stained amniotic fluid; 1- or 5-minute Apgar scores; and neonatal gender and birth weight.
There were three cases of symptomatic uterine rupture, all in the group with interdelivery interval greater than 19 months, but this difference was not significant (P = 1.00). This rate of uterine rupture is consistent with those reported in the literature.1 We found no other significant maternal or neonatal morbidity. No data were available with respect to clinical practice or uterine closure. However, no significant changes in labor management were evident at the two centers during the study period.
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DISCUSSION |
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Incomplete healing of the uterine scar from a previous cesarean delivery, as a result of short interdelivery interval, has been suggestive as a risk factor for uterine rupture during a trial of VBAC. Shipp et al supported this idea, in a report of increased rate of uterine rupture during a trial of labor, in VBAC patients with interdelivery interval less than 18 months compared with those with longer intervals.8 Esposito et al also observed an increase in the rate of uterine rupture with short interdelivery intervals.9 Potentially, a short interdelivery interval can adversely affect uterine activity during labor as a result of the inadequate postpartum healing of the previous cesarean scar.
Characteristics associated with successful trials of labor after cesarean delivery have been extensively studied.10–12 However, no study has been conducted to specifically address the potential relationship between interdelivery interval and the rate of VBAC success, according to a MEDLINE search from 1966 to August 2001 using the terms "interdelivery interval" and "VBAC." In our study, the rate of VBAC success did not appear to be affected by the interdelivery interval between prior cesarean delivery and the index pregnancy. Furthermore, there was no increase in the rate of symptomatic uterine rupture in those patients with shorter interdelivery intervals, although this finding may be limited by the sample size.
A short interdelivery interval was associated with a decrease in the rate of successful VBAC in patients whose labors were induced, a difference not found in those who underwent spontaneous labor. Perhaps spontaneous labor represents the complete healing of the uterine scar, enabling the uterus to adequately respond to the hormonal milieu that causes the spontaneous progression of labor. We must be cautious when interpreting this information, however. Because of the small number of patients in the group with interdelivery interval less than 19 months, the significance of this association is unclear.
Although it appears that the healing of the lower uterine segment cesarean scar occurs promptly postpartum in most patients, and does not seem to interfere with the normal physiologic and anatomic changes that transpire during subsequent labor and delivery, the safety of VBAC remains debatable. We demonstrated a potential association between interdelivery interval and success of VBAC, specifically in patients who undergo labor induction. Nevertheless, the clinical importance cannot be definitely established by our retrospective study design. Obstetricians should continue to counsel patients regarding trial of VBAC based on current established guidelines.
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Footnotes |
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Received June 5, 2001. Received in revised form September 4, 2001. Accepted September 17, 2001.
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REFERENCES |
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2. Scott JR. Mandatory trial of labor after cesarean delivery: An alternative viewpoint. Obstet Gynecol 1991;77:811–4.
3. Phelan JP. VBAC: Time to reconsider? OBG Manage 1996:62–8.
4. Schwarz O, Paddock R, Bortnick AR. The cesarean scar: An experimental study. Am J Obstet Gynecol 1938;36: 962.
5. Wojdecki J, Grynsztajn A. Scar formation in the uterus after cesarean section. Am J Obstet Gynecol 1970;107: 322–4.[Medline]
6. Dicle O, Kucukler C, Pirnar T, Erata Y, Posaci C. Magnetic resonance imaging evaluation of incision healing after cesarean sections. Eur Radiol 1997;7:31–4.[Medline]
7. McMahon MJ, Luther ER, Bowes WA Jr, Olshan AF. Comparison of a trial of labor with an elective second cesarean section. N Engl J Med 1996;335:689–95.
8. Shipp TD, Zelop CM, Repke JT, Cohen A, Lieberman E. Interdelivery interval and risk of symptomatic uterine rupture. Obstet Gynecol 2001;97:175–7.
9. Esposito MA, Menihan CA, Malee MP. Association of interpregnancy interval with uterine scar failure in labor: A case-control study. Am J Obstet Gynecol 2000;183: 1180–3.[Medline]
10. Troyer LR, Parisi VM. Obstetric parameters affecting success in a trial of labor: Designation of a scoring system. Obstet Gynecol 1992;167:1099–104.
11. Weinstein D, Benshushan A, Tanos V, Zilberstein R, Rojansky N. Predictive score for vaginal birth after cesarean section. Am J Obstet Gynecol 1996;174:192–8.[Medline]
12. Marshak JD, Cooperman BS, Fried WB, Shi Q. Prognostic indicators for successful vaginal birth after cesarean delivery. Obstet Gynecol 2000;95:S38.
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