Prior studies have noted the importance of encouraging TOLAC in reducing the CD rate and improving maternal and child outcomes6. Several reports have shown that using the Generalizing Grobman’s model to predict the success rate of TOLAC in the Chinese population also has a strong clinical predictive power13 15. However, the inclusion population of these studies lacks uniform standards. Given the vigorous promotion of clinical guidelines for obstetrics in China in recent years to reduce medical disputes and improve healthcare quality, it is very important to select patients to be predicted based on clinical guidelines, since the prediction models should be applied only to patient populations selected with similar inclusion and exclusion criteria and clinical management16. The target of the project was to identify the factors that influence the success rate of TOLAC and to develop a predictive model during the implementation of clinical guidelines. Based on the external verification of the widely used Grobman’s model, through the improvement of the Grobman’s model, the corresponding features before delivery were added, the predictive model of this study shows a good prediction ability.
While a clear trend of benefit from the successful vaginal delivery among those trials of labor after cesarean, it should be noted that VBAC failure increases many risks, such as bleeding, blood transfusions, uterine rupture and endometritis, and infant asphyxia or perinatal death8 17 18. Due to the complex physician-patient relationship and the increase in work-related stress, Obstetricians prefer a more conservative approach during TOLAC to avoid medical disputes. When longer labor course or changes in fetal heart rate occur during TOLAC, doctors are more active to take repeat cesarean section to avoid the adverse consequences of uterine rupture or neonatal asphyxia. For this reason, as the results show, the incidence of adverse clinical outcomes such as uterine rupture and neonatal asphyxia is lower than the related literature. However, this strategy also reduces the success rate of TOLAC accordingly.
In this study, the risk model described has several advantages in its discrimination and calibration compared to Grobman’s model, by increasing and selecting the predictor variable near delivery.
The inclusion and exclusion criteria of this study were based on recent clinical guidelines, and the pre-delivery variables were increased by modifying the Grobman’s model. These results are in accord with recent studies indicating maternal BMI at delivery, history of vaginal delivery and maternal age at delivery are relevant or independent risk factors for the success of TOLAC12 19-22. Among these factors, history of vaginal delivery can be used to predict TOLAC success was not in dispute23. Even if the proportion of older pregnant women increased affected by China’s recent two-child policy, we still find that maternal age is correlated with the success of TOLAC. Given the differences in BMI between different races 24, maternal BMI as a continuous variable included in the model. The results of LASSO screening showed that maternal pre-pregnancy weight is not an independent risk factor for TOLAC's success, and the maternal weight at delivery has a correlation with the success rate.
Bishop’s score is a relatively subjective indicator, for standardization, we looked up the cervical bishop’s score two hours after regular uterine contractions, and checked the results of midwives and obstetricians at the same time, and averaged them. We found a positive correlation between Bishop’s score and success of TOLAC. This finding is consistent with that of Francis(2005) who declare that risk of cesarean delivery related to an unfavourable Bishop score at admission25. Similarly, several studies confirms that the Bishop’s score at delivery affects the success rate of TOLAC17 26. The OR of Bishop’s score in this investigation were higher and have relatively narrow confidence intervals compared to those of other studies and have(OR, 3.27; 95% CI, 2.49 to 4.55). It is possible that previously reported models may underestimate the role of standardized cervical evaluation.
Maternal pelvis shape and fetal weight are the determining factor for the success of TOLAC13 21, however, both of them are hard to estimate, in general. A strong relationship between maternal pelvis shape and their height has been reported in the literature27. Corresponding to this result, in this study pregnant women with higher heights seem to have a greater chance of TOLAC success. Hence, it could conceivably be hypothesised that maternal height is an independent factor that influences the success of TOLAC. Determine fetal weight by ultrasound scan is difficult to obtain high accuracy, and easily affected by the experience of ultrasound doctors28. In addition, ultrasound scan is difficult to standardize the estimated weight between different hospitals, so we chose the fundal height and maternal abdominal as the indicators to included it in the model, and noted fundal height showed a negative correlation with TOLAC success.
It has been suggested that Using pregnancy at 40 weeks as the cut-off point to develop a prediction model29 30. However, for reference the clinical guidelines, in the present study we used a cutoff of 39 weeks for delivered gestational weeks. However, for reference the clinical guidelines, in the present study we used a cutoff of 39 weeks for delivered gestational weeks. Interestingly, the similar results were observed for using these difference cut-off values: the later of gestational weeks, the lower the success rate of TOLAC.
Although studies have implicated the hysterotomy scar can predict the success of TOLAC31,we did not evaluate performance on the hysterotomy scar. Due to this examination is difficult to standardize and is not conducive to further promotion to the primary hospital because of the difference in the experience of ultrasound doctors and examination methods. Recent evidence also suggests that the prediction model based on the sonographic assessment of a hysterotomy scar demonstrated poor accuracy for the prediction of successful VBAC32.
Finally, this study had several limitations, including those inherent to the study design, particularly those dependent on retrospective recall of medical services received. Although we screened all vaginal trial cases during the study period, some patients refusal TOLAC and select repeat cesareans. Secondly, the sample size limited includes more clinical factors to prediction models for improvement of accuracy. Third, since this study is a single center study in Southeast China, additional researches should be conducted to amend and verify the predict model for fully promoted in China.