Trial of Labour (TOL / TOLAC / VBAC)

Trial of Labour After Caesarean (TOLAC) refers to allowing a woman with a previous uterine scar (most commonly from caesarean delivery) to attempt vaginal birth in a subsequent pregnancy. Successful vaginal delivery in this context is called Vaginal Birth After Caesarean (VBAC).

Definition and Background

A trial of vaginal birth after a previous caesarean delivery (VBAC) is an accepted method of delivery for most women with a prior low-transverse caesarean incision. In the 1980s, VBAC rates rose sharply in response to efforts to control the rising caesarean rate. When properly selected and managed, 7-8 out of 10 women with uterine scars will deliver vaginally.

Among women who attempt TOLAC in contemporary US practice, approximately 57% achieve successful vaginal birth
Only 28.8% of women with a prior caesarean actually attempt vaginal birth (Zhang et al.)

(Creasy & Resnik's Maternal-Fetal Medicine, p. 963; Textbook of Family Medicine 9e, p. 513)

Indications / Candidates for TOLAC

The following women are generally good candidates for TOLAC (SOR: A):

One prior low-transverse caesarean incision
Nonrecurrent indication for previous caesarean (e.g. breech, placenta praevia - not CPD/failure to progress)
Previous vaginal birth (strongest positive predictor of success)
Spontaneous onset of labour
Age < 40 years
Estimated fetal weight ≤ 4000 g
Adequate pelvis / no clinical CPD

Women with a low vertical incision that does not extend into the fundus are also candidates (SOR: B).

Contraindications

TOLAC is contraindicated in (SOR: C):

Absolute Contraindications	Notes
Previous classic (fundal) uterine incision	Very high rupture risk
Extensive transfundal uterine surgery	e.g. myomectomy through uterine cavity
Previous uterine rupture	Recurrence risk
Inability to perform emergency caesarean	Facility/personnel limitations

Use of misoprostol (PGE1) for cervical ripening in women with a prior caesarean is associated with significantly increased uterine rupture risk and should be avoided in the third trimester (SOR: A)
Use of prostaglandins in general for cervical ripening or labour induction should be discouraged

Predictors of Successful VBAC

Women most likely to achieve VBAC:

Spontaneous onset of labour
One prior vaginal delivery
Nonrecurrent indication for prior caesarean
Baby ≤ 4000 g
Age < 40 years
Prior caesarean was NOT for active-phase failure to progress or CPD

Women with >80% probability of successful vaginal delivery have the overall risk of TOLAC substantially reduced because most major complications occur in those who fail and ultimately require emergency caesarean.

Key Risk: Uterine Rupture

This is the primary concern with TOLAC.

Scar Type	Rupture Risk
Low-transverse (classic LSCS)	0.5% - 1.0%
Low vertical (within lower segment)	Low but less data
Classic/fundal incision	Much higher (3-9%)

Clinical signs of uterine rupture:

Fetal heart rate decelerations / fetal distress (most common early sign)
Heavy vaginal bleeding
Decreasing fetal station or complete loss of presenting part
Loss of contraction intensity (on internal uterine pressure monitor)
Uterine/pelvic pain between contractions
Bloody urine (haematuria)

From a large cohort of >30,000 women (Landon et al.):

Symptomatic uterine rupture occurred in 0.7% of TOLAC women
12 infants in the TOLAC group developed encephalopathy; none in the elective repeat caesarean group
7 of those 12 encephalopathy cases were directly associated with uterine rupture (rate 0.46/1000 TOLAC)
Rates of endometritis and transfusion were higher in TOLAC group
No difference in hysterectomy or maternal death rates

(Creasy & Resnik's, p. 963)

Management of TOLAC

Facility Requirements

TOLAC should only be attempted in institutions equipped to respond to emergencies with physicians immediately available to provide emergency care (AAFP recommendation)

Labour Management

Oxytocin: Not contraindicated, but use cautiously; an internal uterine pressure monitor is recommended when labour is augmented or induced
Epidural analgesia: Not contraindicated and may be used (SOR: A). Concern that it masks rupture pain is not well-supported by evidence; epidural does not reliably obscure symptoms of rupture
Electronic fetal monitoring: Continuous monitoring is standard, as fetal decelerations are the earliest sign of rupture
Internal uterine pressure monitoring: Recommended when labour is medically enhanced

Counselling

Informed consent and full discussion of risks and benefits must be documented
25% of women choose elective repeat caesarean even when TOLAC is offered and they are good candidates
Three decision archetypes exist: those who strongly prefer vaginal birth, those who prefer repeat caesarean due to prior experience, and those who are ambivalent and most responsive to professional guidance

Comparing TOLAC vs. Elective Repeat Caesarean Section (ERCS)

Outcome	TOLAC	ERCS
Vaginal delivery	~57-80%	0%
Uterine rupture	0.5-1%	Very rare
Major maternal complications	OR 1.8 (if TOLAC fails)	Baseline
Endometritis	Higher	Lower
Perinatal death (labour-related)	12.9/10,000	~1.2/10,000 (Scotland data)
Future placenta praevia/accreta	Lower	Higher with each repeat CD
Neonatal respiratory morbidity	Lower (labour beneficial)	Higher (especially at 37-38 weeks)

Overall: The outcomes are so similar that the two approaches are considered medically equivalent on a population basis. Women's preferences, circumstances, and values should drive the final decision.

Special Situations

Two prior low-transverse caesareans: Insufficient evidence to clearly recommend TOLAC; most centres consider it cautiously. A 2024 meta-analysis (PMID 38485519) specifically examined this question.
Twin gestation: Small series suggest no greater complication incidence than singleton VBAC, but data are limited
Breech presentation: Limited case series; continued caution recommended
Post-term pregnancy: Limited data; approach with caution
Macrosomia (>4000 g): Increased failure rate; information insufficient to recommend TOLAC

Recent Evidence (2024-2026)

PMID 38485519 (Meta-Analysis, 2024): Trial of labour vs. elective caesarean for patients with two prior caesareans - provides updated evidence for this specific scenario
PMID 41241095 (Meta-Analysis, 2026): Oxytocin dosing during TOLAC to minimise uterine rupture risk - important for labour management protocols

Note: A 2026 meta-analysis on oxytocin dosing during TOLAC (PMID 41241095) may offer updated guidance on safe oxytocin use, which could refine the "cautious use" recommendation above.

Sources: Textbook of Family Medicine 9e, p. 512-513; Creasy & Resnik's Maternal-Fetal Medicine, pp. 959-963

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