What are your chances of a successful VBAC?

Whether you are considering a VBAC (vaginal birth after caesarean - pronounced 'Vee-back') at home or in hospital, this page looks at your chances of having a vaginal birth, versus ending up with another caesarean.

It could be particularly relevant for women planning home VBACs, as the decision of whether or not to book a home birth might depend partly on how likely you are to need a repeat caesarean anyway, or to transfer to hospital for other reasons.

Remember that these studies can only give you an idea of probabilities, and that there are many aspects they do not take account of - such as your general state of health, fitness, or any ante-natal preparation you might have done. Studies show us what outcomes to expect over large numbers of people, but they do not determine the outcome in any particular case. You are an individual, and your uterus might not have read all the research which suggests how it should act!

At what point in labour did the mother have her caesarean?

Some studies have found that your chances of a vaginal birth after caesarean depend partly on how far the last labour progressed before the caesarean was performed. If you had any degree of dilation at all then, next time around, dilation up until that point at least should progress more smoothly.

Correlation between maximum cervical dilatation at cesarean delivery and subsequent vaginal birth after cesarean delivery.

Hoskins IA, Gomez JL
Obstet Gynecol 1997 Apr;89(4):591-3

This study looked at the VBAC rate for 1917 women attempting VBAC in New York. It found that the chances of a successful VBAC were:

It concluded: "Patients who attempt a VBAC may be counseled that a cesarean delivery at full dilatation is associated with a reduced chance of a subsequent successful VBAC"

However, the next study looked more closely at women who had caesareans for their first babies, specifically for lack of progress in the second stage of labour. This was often after a failed attempt at instrumental delivery (ie with forceps or ventouse). It reached quite different conclusions.

Medline abstract: Hoskins and Gomez (1997)

Vaginal delivery after previous caesarean section for failure of second stage of labour.

Jongen VH, Halfwerk MG, Brouwer WK
Br J Obstet Gynaecol 1998 Oct;105(10):1079-81

The study looked at 103 women who attempted a VBAC after having a caesarean in the second stage of labour. The VBAC rates were:

Conclusion: “In women with a cephalic presentation who had an arrest of descent in the second stage of labour during their first delivery, the chances of vaginal delivery in their next pregnancy are high, even after a failed instrumented vaginal delivery, and a trial of labour can usually be pursued.”

Medline abstract: Jongen, Halfwerk, Brouwer (1998)

Lack of progress in the second stage might be treated as a sign that the baby was really too big to be born through the mother's pelvis - that there was true cephalo-pelvic disproportion. After all, if the cervix is fully dilated, what's stopping the baby from coming out? And if she has a failed instrumental delivery, so even forceps of ventouse could not make the baby budge, what else could explain it?

Perhaps the mother is exhausted and unable to push, perhaps she is in a position which reduces the room for the baby to be born (eg on her back or propped up), or perhaps her body is simply taking a long rest - a 'latent phase' before pushing the baby out. Perhaps the baby was in a difficult position, such as posterior or face presentation. Perhaps the baby went into distress for some reason, and needed to be delivered immediately. Many of the possible explanations are things that need not be repeated for the mother's next birth.

So why did these two studies reach such different conclusions? UK obstetrician Danny Tucker (of the Women's Health website) said "Something tells me that it has something to do with the differences in labour management between University Medical Centre, New York and practices in the Netherlands" (post on misc.kids.pregnancy newsgroup)

What was the reason for the previous Caesarean?

The study by Hoskins and Gomez mentioned above gave more details about what the previous c/s was for, compared to the VBAC rate for the next baby. The VBAC rates were:

Attempt and success rates for vaginal birth after caesarean section in relation to complications of the previous pregnancy

Holt VL, Mueller BA
Paediatr Perinat Epidemiol 1997 Jan;11 Suppl 1:63-72

This study looked at 10,110 in Washington State, USA, who had a caesarean for their first baby. The women most likely to attempt a VBAC with their second child were those whose first c/s had been performed after induced labour, for genital herpes, for fetal distress, or for breech presentation. On the other hand, the women whose first c/s was for a large baby, apparent cephalopelvic disproportion, prolonged labour, diabetes or problems with the placenta, were less likely to attempt a VBAC.

This means that the group of women who attempted VBAC is not fully representative of all women who have had a caesarean - arguably, the women who might have been less likely to have a VBAC, did not attempt one. Overall 64% of the women attempted a VBAC, and of those women, 62% did give birth vaginally. Of the women who attempted a VBAC:

Medline abstract: Holt and Mueller (1997)

Vaginal birth after cesarean: a meta-analysis of indicators for success.

Rosen MG, Dickinson JC
Department of Obstetrics and Gynecology, Sloane Hospital for Women, New York, New York.
Obstet Gynecol 1990 Nov;76(5 Pt 1):865-9

This paper was a meta-analysis of 29 individual studies, looking at the chances of a successful VBAC according to various factors.

The abstract gives odds ratios for a VBAC, instead or percentages or ratios, which are more common. An explanation of odds ratios is available.

The meta-analysis found that:

Where the previous CS was for apparent cephalopelvic disproportion, the odds were 0.5 for a successful trial of labor. This means that for every woman who had a VBAC, two attempted one but ended up with a repeat c/s - so the percentage of women who had a VBAC was about 33%.

If the previous CS was for a breech baby, the odds of VBAC were 2.1. So a VBAC attempt was more than twice as likely to be successful as not (about 68%).

For women receiving oxytocin, the odds were 0.3 - ie about 23%.

Conclusion: "Even though the success rates do vary with the different preexisting factors, the clinician may anticipate a greater than 50% chance for success in any individual labor."

Medline abstract: Rosen and Dickinson (1990)

Ever had a vaginal birth?

If the mother has previously had a vaginal birth, perhaps before her caesarean, then her chances of VBAC are higher. This may partly reflect confidence among midwives and doctors, as well as for the mother, that she can give birth vaginally. There will not be worries about an 'untried pelvis' for example.

The study by Rosen and Dickinson, above, found that for the women with a previous vaginal birth as well as a previous c/s, the odds of VBAC were 2.1 (about 68% success rate).

Although uterine rupture is rare, it is now known that once you have had one VBAC, your chances of rupturing during a future VBAC attempt are lower. This is important, as women who have already had one VBAC are sometimes worried that their scar will have been put under stress by the first labour, and so might be weaker next time around. So, if you have already had one vaginal birth following your caesarean, you are in a lower-risk category for rupture than a woman whose scar has not been 'tested' by labour.

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
Isr Med Assoc J 2000 Jul;2(7):526-8

"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."

Medline Abstract: Shimonovitz, Botosneano, Hochner-Celnikier (2000)

Obstet Gynecol. 2008 Feb;111(2 Pt 1):285-91.

Labor outcomes with increasing number of prior vaginal births after cesarean delivery.

Mercer BM, Gilbert S, Landon MB, Spong CY, Leveno KJ, Rouse DJ, Varner MW, Moawad AH, Simhan HN, Harper M, Wapner RJ, Sorokin Y, Miodovnik M, Carpenter M, Peaceman A, O'Sullivan MJ, Sibai BM, Langer O, Thorp JM, Ramin SM;
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 ... 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. PMID: 18238964 [PubMed - indexed for MEDLINE]

The next study, by Caughey et al, found that mothers who had a vaginal birth after the caesarean were more likely to get another VBAC than mothers who'd only had a vaginal birth before the caesarean. This just sounds like common sense to me!

Trial of labor after cesarean delivery: the effect of previous vaginal delivery.

AUTHORS: Caughey AB; Shipp TD; Repke JT; Zelop C; Cohen A; Lieherman E
Am J Obstet Gynecol 1998 Oct;179(4):938-41.
"The rates of cesarean delivery for the vaginal last and cesarean last groups were 7.2% and 14.7%, respectively. The median durations of labor for the vaginal last and cesarean last groups were 5.6 and 7.0 hours, respectively. The differences in cesarean rates and durations of labor were seen regardless of the indication for the previous cesarean delivery."

Medline Abstract for this study: Caughey, Shipp et al, 1998

VBAC when 'overdue'

Safety and efficacy of attempted vaginal birth after cesarean beyond the estimated date of delivery.

Callahan C ; Chescheir N ; Steiner BD
J Reprod Med, 44(7):606-10 1999 Jul

This study looked at women who attempted VBAC after their due dates. It compared 90 women who attempted VBAC in 1995-1996 with 90 other women matched for age, race and parity, but without a previous caesarean. It found that:

CONCLUSION:"The patient and her family can be reassured that passing her due date does not alter the efficacy or safety of a trial of labor. No change in counseling is warranted simply due to the completion of 40 weeks' gestation"

Medline abstract

Two or more caesareans?

Please see the page dedicated to this subject - VBA2C (vaginal birth after two caesareans).

This page last updated 22 August 2001


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