VBAC After Prior VBAC: Decreased Risks, Not Increased Risks

Just in time for Cesarean Awareness Month, another *headdesk* moment from My OB Said What?!?.

This one is about whether a woman who has already had VBACs should continue to have more VBACs or whether she needs to sign up for more cesareans because having too many VBACs becomes "too dangerous."

"I will not go over this with you and you are being argumentative! More than a few VBACs will be unsafe because the scar stretches and can become unstable. I don't care how many safe VBACs you've had and about any of the other testing you've had in the past, this is dangerous!" --OB to mother trying to VBAC again

Sometimes I can't believe the stupid things that come out of some providers' mouths. With all the research out there disproving the foolish myths that circulate, I can't believe that this is even a question, yet every once in a while we still hear this one in VBAC groups. Sigh.

So let's go over what the research actually says:

• Prior vaginal births actually decrease your risk for rupture (de Lau 2011, Zelop 2000)
• Prior VBACs particularly decrease your risk for uterine rupture (Mercer 2008, Shimonovitz 2000)
• Each successive VBAC does not get more risky  (Mercer 2008)
• Each successive cesarean does get more risky (Silver 2006)
• Grand multiparity (5 or more pregnancies) is not a contraindication to a trial of labor (Kugler 2008) 
• Women with a history of VBAC have a very high success rate in subsequent trials of labor (Mercer 2008, Gyamfi 2004)

Of course, in the interest of accuracy, I would point out that once you've had a cesarean, the risk of uterine rupture is never zero or negligible, even with multiple prior VBACs.  However, the risk is decreased compared to a woman who has never had a VBAC.  And the risk of multiple repeat cesareans is certainly significant.

Given that the risk for rupture goes down somewhat with successive VBACs, given that women with a prior VBAC have a very high success rate in subsequent VBAC attempts, given that grand multiparity is not a contraindication to VBACs, and given that there are strong risks with multiple repeat cesareans, why would doctors limit how many VBACs a woman is "allowed" to have?

Mercer and colleagues stated as much in the conclusion of their study, saying (emphasis mine):

Women with prior successful VBAC attempts are at low risk for maternal and neonatal complications during subsequent VBAC attempts. An increasing number of prior VBACs is associated with a greater probability of VBAC success, as well as a lower risk of uterine rupture and perinatal complications in the current pregnancy. There is no reason to place a limit on the number of VBACs a woman can have.

That research was published in 2008.  It's long past time for the entire obstetric community to get the memo on this.


References

Mercer BM, Gilbert S, Landon MB. et al. Labor Outcomes With Increasing Number of Prior Vaginal Births After Cesarean Delivery. Obstet Gynecol. 2008 Feb;111(2):285-291.  PMID:  18238964   You can read the entire study here.

OBJECTIVE: To estimate the success rates and risks of an attempted vaginal birth after cesarean delivery (VBAC) according to the number of prior successful VBACs. METHODS: From a prospective multicenter registry collected at 19 clinical centers from 1999 to 2002, we selected women with one or more prior low transverse cesarean deliveries who attempted a VBAC in the current pregnancy. Outcomes were compared according to the number of prior VBAC attempts subsequent to the last cesarean delivery. RESULTS:  Among 13,532 women meeting eligibility criteria, VBAC success increased with increasing number of prior VBACs: 63.3%, 87.6%, 90.9%, 90.6%, and 91.6% for those with 0, 1, 2, 3, and 4 or more prior VBACs, respectively (P<.001). The rate of uterine rupture decreased after the first successful VBAC and did not increase thereafter: 0.87%, 0.45%, 0.38%, 0.54%, 0.52%(P=.03). The risk of uterine dehiscence and other peripartum complications also declined statistically after the first successful VBAC. No increase in neonatal morbidities was seen with increasing VBAC number thereafter. CONCLUSION: Women with prior successful VBAC attempts are at low risk for maternal and neonatal complications during subsequent VBAC attempts. An increasing number of prior VBACs is associated with a greater probability of VBAC success, as well as a lower risk of uterine rupture and perinatal complications in the current pregnancy.

Arch Gynecol Obstet. 2011 Nov;284(5):1053-8. Epub 2011 Aug 31. Risk of uterine rupture in women undergoing trial of labour with a history of both a caesarean section and a vaginal delivery. de Lau H, Gremmels H, Schuitemaker NW, Kwee A. PMID: 21879334

PURPOSE: To determine the risk of uterine rupture for women undergoing trial of labour (TOL) with both a prior caesarean section (CS) and a vaginal delivery. METHODS: A systematic literature search was performed using keywords for CS and uterine rupture. The results were critically appraised and the data from relevant and valid articles were extracted. Odds ratios were calculated and a pooled estimate was determined using the Mantel-Haenszel method. RESULTS: Five studies were used for final analysis. Three studies showed a significant risk reduction for women with both a previous CS and a prior vaginal delivery (PVD) compared to women with a previous CS only, and two studies showed a trend towards risk reduction. The absolute risk of uterine rupture with a prior vaginal delivery varied from 0.17 to 0.46%. The overall odds ratio for PVD was 0.39 (95% CI 0.29-0.52, P < 0.00001). CONCLUSION: Women with a history of both a CS and vaginal delivery are at decreased risk of uterine rupture when undergoing TOL compared with women who have only had a CS.

Obstet Gynecol. 2004 Oct;104(4):715-9. Increased success of trial of labor after previous vaginal birth after cesarean. Gyamfi C, Juhasz G, Gyamfi P, Stone JL.  PMID: 15458891

OBJECTIVE: To estimate whether a history of a previous successful vaginal birth after cesarean delivery (VBAC) has an effect on a subsequent VBAC attempt...RESULTS: Of the 336 patients with a history of one or more previous successful VBAC attempts, 94.6% had a subsequent successful VBAC, whereas 70.5% of the remaining 880 patients were successful (P <.001). For those patients with one or more previous successful normal spontaneous vaginal deliveries, 87.8% had a successful VBAC, whereas 75.6% were successful without this history (P =.001)...Patients with a history of previous VBAC were 7 times more likely to have a subsequent VBAC success (odds ratio 7.40, 95% confidence interval 4.51-12.16; P <.001)...CONCLUSION: A history of a previous successful VBAC increases the likelihood for success with future attempts....

Isr Med Assoc J 2000 Jul;2(7):526-8. Successful first vaginal birth after cesarean section: a predictor of reduced risk for uterine rupture in subsequent deliveries. Shimonovitz S, Botosneano A, Hochner-Celnikier D.  PMID: 10979328

BACKGROUND: Uterine rupture is a catastrophic obstetric complication, most often associated with a preexisting cesarean section scar. Although a vaginal birth after a cesarean is considered safe in modern obstetrics, it is not known whether repeated VBACs increase the risk of rupture, or whether the first VBAC proves the strength and durability of the scar, predicting further successful and less risky vaginal deliveries. OBJECTIVES: To evaluate the effect of repeated vaginal deliveries on the risk of uterine rupture in women who have previously delivered by cesarean section. METHODS: In this retrospective study, 26 VBAC deliveries complicated by uterine rupture were matched for age, parity, and gravidity with 66 controls who achieved VBAC without rupture. The histories, demography, pregnancy, labor and delivery records, as well as neonatal outcome were compared. RESULTS: We found that the risk of rupture decreases dramatically in subsequent VBACs. Of the 40 cases of uterine rupture recorded during the 18 year study period, 26 occurred during VBAC deliveries. Of these, 21 were complicated first VBACs. We also found that the use of prostaglandin-estradiol, instrumental deliveries, and oxytocin had been used significantly more often during deliveries complicated with rupture than in VBAC controls. CONCLUSIONS: Once a woman has achieved VBAC the risk of rupture falls dramatically. The use of oxytocin, PGE2 and instrumental deliveries are additional risk factors for rupture, therefore caution should be exerted regarding their application in the presence of a uterine scar, particularly in the first vaginal birth after cesarean.

Am J Obstet Gynecol. 2000 Nov;183(5):1184-6. Effect of previous vaginal delivery on the risk of uterine rupture during a subsequent trial of labor. Zelop CM, Shipp TD, Repke JT, Cohen A, Lieberman E.  PMID: 11084564

OBJECTIVE: We examined the effect of prior vaginal delivery on the risk of uterine rupture in pregnant women undergoing a trial of labor after prior cesarean delivery. STUDY DESIGN: The medical records of all pregnant women with a history of cesarean delivery who attempted a trial of labor during a 12-year period at a single center were reviewed...RESULTS: Of 3783 women with 1 prior scar, 1021 (27.0%) also had > or =1 prior vaginal delivery. During a subsequent trial of labor, the rate of uterine rupture was 1.1% among pregnant women without prior vaginal delivery and 0.2% among pregnant women with prior vaginal delivery (P =.01). Logistic regression analysis controlling for duration of labor, induction, birth weight, maternal age, year of birth, epidural analgesia, and oxytocin augmentation indicated that, among women with a single scar, those with a prior vaginal delivery had a risk of uterine rupture that was one fifth that of women without a previous vaginal delivery (odds ratio, 0.2; 95% confidence interval, 0.04-0.8)...CONCLUSION: Among women with 1 prior cesarean delivery undergoing a subsequent trial of labor, those with a prior vaginal delivery were at substantially lower risk of uterine rupture than women without a previous vaginal delivery.

Archives of Gynecology and Obstetrics. 2008 Apr;277(4):339-44. The safety of a trial of labor after cesarean section in a grandmultiparous population. Kugler E, Shoham-Vardi I, Burstien E, Mazor M, Hershkovitz R.  PMID: 17957377 

BACKGROUND: The rate of vaginal birth after a cesarean (VBAC) delivery in the multiparous population has decreased largely in recent years because of maternal and neonatal complications. The clinical management of grand multiparous (GMP) women (>5 births) with a prior cesarean delivery is even less clear. The purpose of the present study was to assess the risks of maternal and neonatal complications associated with VBAC compared to that of repeated elective cesarean section (CS) in the GMP population. METHODS: A retrospective study of 1,102 GMP women with a singleton gestation and a prior single CS was conducted. Data were retrieved from the database of the Department of Obstetrics and Gynecology at the Soroka University Medical Center, Beer Sheva, Israel. Maternal and neonatal outcomes were compared between women who underwent a successful VBAC attempt, women who had failed in a trial of labor and women who had an elective repeated CS. RESULTS: Six hundred and nineteen women (56%) underwent a successful VBAC, 155 (14%) underwent a trail of labor and 328 (30%) had an elective repeated CS. Women who had a successful VBAC required less blood transfusion, and had less puerperal fever diseases (P < 0.001). Induction or augmentation of labor was associated with failure of VBAC (P < 0.001). No significant differences in neonatal complications were observed between the groups. No significant difference in uterine dehiscence, uterine rupture, amnionitis, postpartum hemorrhage, hysterectomy, puerperal fever and thromboembolic diseases was observed between the groups. CONCLUSIONS: A successful VBAC in the GMP population was not associated with a higher risk of maternal complications in comparison with a repeated elective CS.

Obstet Gynecol. 2006 Jun;107(6):1226-32. Maternal morbidity associated with multiple repeat cesarean deliveries. Silver RM, Landon MB, Rouse DJ, Leveno KJ, Spong CY, Thom EA, Moawad AH, Caritis SN, Harper M, Wapner RJ, Sorokin Y,Miodovnik M, Carpenter M, Peaceman AM, O'Sullivan MJ, Sibai B, Langer O, Thorp JM, Ramin SM, Mercer BM; National Institute of Child Health and Human Development Maternal-Fetal Medicine Units Network. PMID: 16738145

...METHODS: Prospective observational cohort of 30,132 women who had cesarean delivery without labor in 19 academic centers over 4 years (1999-2002). RESULTS: There were 6,201 first (primary), 15,808 second, 6,324 third, 1,452 fourth, 258 fifth, and 89 sixth or more cesarean deliveries. The risks of placenta accreta, cystotomy, bowel injury, ureteral injury, and ileus, the need for postoperative ventilation, intensive care unit admission, hysterectomy, and blood transfusion requiring 4 or more units, and the duration of operative time and hospital stay significantly increased with increasing number of cesarean deliveries. Placenta accreta was present in 15 (0.24%), 49 (0.31%), 36 (0.57%), 31 (2.13%), 6 (2.33%), and 6 (6.74%) women undergoing their first, second, third, fourth, fifth, and sixth or more cesarean deliveries, respectively. Hysterectomy was required in 40 (0.65%) first, 67 (0.42%) second, 57 (0.90%) third, 35 (2.41%) fourth, 9 (3.49%) fifth, and 8 (8.99%) sixth or more cesarean deliveries. In the 723 women with previa, the risk for placenta accreta was 3%, 11%, 40%, 61%, and 67% for first, second, third, fourth, and fifth or more repeat cesarean deliveries, respectively. CONCLUSION: Because serious maternal morbidity increases progressively with increasing number of cesarean deliveries, the number of intended pregnancies should be considered during counseling regarding elective repeat cesarean operation versus a trial of labor and when debating the merits of elective primary cesarean delivery.