This study was conducted with the main objective of identifying factors associated with successful vaginal delivery on mothers offered trial of labour after previous lower segment caesarean section. Significant Determinants found were history of still birth, history of successful VBAC, past indication of past C/S, presence of meconium, cervical dilatation at admission, rupture of membrane at admission and its duration and position of the presenting part. In this study parity, maternal age, gestational age, medical illness, HIV status, inter delivery interval, history of SVD, and birth weight were not found significant determinants.
The strengths of this study were the methodology, the use of inclusion and exclusion criteria. The case ascertainment and analyzing variables with less missing value has added to the strength.
There were some limitations in this study the study might be affected from small sample size effect because of errors made on the assumptions while calculating the sample size. There could also be a possibility of recall bias at reporting the inter delivery interval and indications of past cesarean section. Documentation on important variables, like occupational status, educational status, Apgar score, blood loss, post delivery hematocrit and medical illness was not good which has made these variables to be excluded from analysis.
Young maternal age and primiparity were associated with high success rate with vaginal delivery even though the bivariate analysis didn’t show that. Similar findings have also been reported by other authors [9
]. Gestational age was not found a significant predictor of success in this study. There are reports which found that gestational age above 40 weeks is associated with poor success [4
]. In our case the finding could also be confounded by high number of unknown dates and ascertainment of correct date was not possible.
History of still birth was one parameter which was associated with poor success in this study. This could be arising from the assumption that the cesarean route of delivery would give the mother a higher chance of having alive baby. Inter delivery interval was not associated with success of delivery. On other reports it was found that interval of less than 2 years was associated with poor success but not in our case [3
]. This could be partly due to difficulty of case ascertainment and recall bias. Those mothers with unknown indications for past cesarean section have been found amazingly associated with high success. From known indications fetal distress, malpresentations and failed induction were associated with poor success. Breech presentation was not found significant determinant as opposed to other reports which consistently reported favoring successful vaginal delivery because of its less recurrence [3
Prior successful VBAC was found to be associated with success which is similar to other reports [1
]. Many authors reported history of prior spontaneous vaginal delivery as important determinant for success in VBAC. But our study failed to show that.
Status of membrane at admission was found to be important factor in predicting success of VBAC. Mothers admitted with rupture of membrane had a higher likelihood of success. But those whose liquor was stained with meconium have poor success.
The strongest factor determining success in this study was cervical dilatation at admission. Those who were admitted with cervical diameter greater 3 cm (Active first stage of labour) had a strong likelihood of vaginal delivery than those admitted at cervical diameter of less than or equal to 3 cm (latent first stage of labour). This is due to high frequency of false labour and slow progress in the latter. This is also supported by the finding that the mean cervical diameter at the time of cesarean section for failed VBAC group 4cm. The other important factor determining success was the position of the presenting part. Those having occipito anterior position were associated with higher success than those with occipito posterior and occipito transverse positions or unknown positions. There was no difference in the birth weight of both groups even though there are reports that macrocosmic babies have poor success. No difference in the neonatal outcome observed in both groups.
66% of repeat caesarean sections (66%) for the failed VBAC group were for reasons of slow progress of labour and arrest of cervical dilatations. This is because, oxytocin augmentation for scarred uterus is not allowed in these hospitals.
Generally the independent variables found to determine success of VBAC found with multivariate analysis were history of absence still birth, history of successful VBAC, cervical diameter at admission more than 3cm, and occipito anterior position of the presenting part (Table
Multivariate analysis of independent variables associated with successful VBAC