Vaginal birth after Caesarean section: review of antenatal predictors of success

Abstract

Objective: To determine antenatal factors that may predict successful vaginal birth after Caesarean (VBAC).

Data sources: The MEDLINE database was searched for all English-language articles describing the impact of various factors on outcomes when VBAC is attempted. Articles reviewed included published abstracts, retrospective and prospective studies, and meta-analyses. CRITERIA FOR STUDY SELECTION: Studies were included if they reported both a control group of pregnant women without the factor under evaluation and a study group with this factor, both undergoing a trial of labour (TOL). Other criteria included accountability for all individuals enrolled at study outset, and vaginal delivery rates in both study and control groups stated or easily calculated.

Results: A nonrecurrent indication for previous Caesarean section (CS), such as breech presentation or fetal distress, is associated with a much higher successful VBAC rate than recurrent indications, such as cephalopelvic disproportion (CPD). Even with a history of CPD, two-thirds of women will have successful VBAC, though rates decrease with increasing numbers of prior CS. Prior vaginal deliveries are excellent prognostic indicators of successful VBAC, especially if the vaginal delivery follows the prior CS. A low vertical uterine incision does not seem to adversely affect VBAC success rates as compared to a low transverse incision. Maternal obesity and diabetes mellitus adversely affect VBAC outcomes. Fetal macrosomia does not appear to be a contraindication to VBAC, as success rates exceeding 50% are achieved and uterine rupture rates are not increased. Twin gestation does not preclude VBAC. Post-dates pregnancies may deliver successfully by VBAC in greater than two-thirds of cases.

Conclusion: There are few absolute contraindications to attempted VBAC. Attempted VBAC will be successful in the majority of attempted cases.