Several studies have reported the association between these individual parameters and morbidity, however, data that have quantified the specific risk given individual patient characteristics are limited. In this study, we developed and validated a model to predict the risk of intrapartum cesarean section based on maternal characteristics, laboratory, and image examination as well as pregnancy complications before a trial of labor. The prediction model is useful to guide clinicians to individually evaluate the risks of intrapartum cesarean section and offer a consultation before the labor trial. The risk factors in this prediction model include older maternal age, shorter in height, longer gestational age, heavier in weight, primipara, lower Bishop score, complicated hypertensive disorder, receiving labor induction and heavier estimation of fetal weight(EFW) within one week before delivery.
After China introduced an overall two-child policy, the proportion of pregnant women with advanced age, obesity, gestational diabetes, gestational hypertension disorder, and other diseases increased, which was accompanied by the increased rate of delivery complications and cesarean section[8]. With the implementation of the New Labor Standard, a prolonged latent period was no longer an indication for cesarean section, hence, puerpera were given more time to have a trial of labor. In clinical practice, for patients with maternal complications as well as those who have one or more risk factors without definite indications of cesarean section, it is necessary to reduce the intervention and give them sufficient trial time based on the New Labor Standard. However, these cases often transform to cesarean section because of arrest active phase, fetal distress, or intrapartum fever, which increases the risk of postpartum hemorrhage and puerperal infection. Thus, there are still various details that need to be explored and improved in clinical practice.
However, there is no risk assessment tool for intrapartum cesarean section at home. Meanwhile, research on attempting to predict the outcome of delivery after labor induction and nulliparous low-risk populations has been reported abroad[9–12]. Most of these models were built based on Western populations, and few models have been applied in clinical practice. Therefore, we innovatively developed two different models to quantify risk factors and predict the risk of intrapartum cesarean section, which can be used to evaluate the labor process in different time nodes, particularly for those with poor progress in the latent period. However, prolonged latent periods did not increase maternal and fetal complications[13]. On the contrary, a prolonged latent period to some degree implied a higher risk of dystocia. Longer duration of the uterine contraction and fetal head compression is associated with increased risks for cervical edema, which entail more cervical examinations, and a high rate of intervention places parturients at significantly greater risk of developing an infection, cervical laceration, fetal distress, and postpartum hemorrhage. Hence, the models we developed may be useful for clinicians to estimate before a trial of labor and reassess the risk during the labor. Meanwhile, for those at high risk of cesarean section, a cesarean section may be elected earlier to avoid "excessive" trial labor and reduce the potential excessive risks of intrapartum cesarean delivery. Otherwise, for those low-risk women, vaginal trial labor should be encouraged, standardized the labor process management, which can reduce the cesarean section rate, and reduce the incidence of vaginal delivery complications.
In this multivariate logistic regression model, parity plays the strongest role in the intrapartum cesarean section, which is a coincidence with previous studies[14]. Compared with the multipara, cervical dilation is relatively slow and the labor process is long in the nulliparous. Tension and fear of parturient can cause an increase in catecholamine secretion, thereby leading to the fluctuation of blood pressure and plasma glucose and eventually to cesarean section because of fetal distress. Maternal age and gestational age may also affect the progress of labor. Therefore, as maternal age increases, the elasticity of tissues decreases and the myometrium becomes less responsive and sensitive to oxytocin, which may extend the labor process and lead to more interventions[15]. With the gradual maturation of the fetus, the skull bone becomes hard, which leads to poor skull overlap during delivery. In addition, the placental function decreases, which may increase the risk of fetal distress or relative cephalopelvic disproportion[16].
Additionally, numerous studies on predicting the outcome of labor induction choose the Bishop score as a predictor, taking it as a good index to evaluate cervical ripening[11,17,18]. However, because of the measurement of the Bishop’s score, some scholars proposed that it was relatively subjective, thereby leaving a problem in light of reproducibility among observers, which was not recommended for risk prediction. Therefore, in some research, the Bishop score was replaced by certain measurements of the cervix by ultrasonography [19,20]. Herein, ultrasound elastography was recently reported to evaluate cervical ripening by quantitatively evaluating the softness and hardness of tissue, however, this technology still needs further research to verify its evaluation efficiency[21]. Ultrasound can accurately measure the length of the cervix, however, it requires suitable training and equipment, which results in limited use to a certain extent. In addition, systematic reviews have no evidence to confirm that ultrasound measurement is superior to Bishop’s score[22,23]. Apart from that, a Guide of the National Institute for Health and Care Excellence currently continues recommending the appraisal of Bishop’s score before induction[24]. In our study, we still use the Bishop’s score as a predictor in model A and stratified the Bishop score. As for model B, given that all patients already enter the active phase, we then excluded the Bishop score and included the latency duration to optimize the model. These two models show good prediction efficiency and can be used in all circumstances.
Moreover, excessive fetal weight leads to intrapartum cesarean section and was used as a predictor in a prior model. However, neonatal birth weight is unknown before the delivery. In this univariate analysis, we found that the estimation of fetal weight measured by ultrasound within one week before the delivery was statistically significant between the vaginal delivery group and the intrapartum cesarean section group. Therefore, we use ultrasound-obtained estimated fetal weight as predictors, thus hoping to reduce postpartum hemorrhage, cervical laceration, and other delivery complications caused by excessive trial labor through this parameter.
Furthermore, most of the patients delivered to our center had regular prenatal examinations, underwent a diagnostic test for gestational diabetes, and had regular blood pressure monitoring. Thus, the rate of missed diagnosis of gestational diabetes and gestational hypertension decreased. Hence, the proportion of gestational diabetes mellitus, hypertensive disorder of pregnancy, and undergoing assisted reproductive technologies is relatively high in our center, and most of them could endure vaginal delivery. Therefore, based on this fact, we studied the relationship between gestational diabetes mellitus, hypertensive disorder of pregnancy, assisted reproductive technologies, and intrapartum cesarean section and eventually include hypertensive disorder of pregnancy and assisted reproductive technologies as predictors in our model.
Despite the high sensitivity and specificity of the multivariate logistic regression model, the calculation process of the model is relatively complex. Consequently, in this study, we converted it into a nomogram, in which all parameters are quantized. Thus, the predicted probability of intrapartum cesarean section can be directly obtained by adding the scores, which have better clinical practicality.
This study uses a large sample size after the new production process standard to build the prediction model. The model, not limited to those low-risk nulliparous, could cover general cases. Furthermore, it is the first time to incorporate the latent period duration as a predictor. Herein, we built two models to evaluate the risk of intrapartum cesarean section at different times of the labor process, which can dynamically assess individual risk and provide a precise prospect of the trial of labor. The predictors include maternal characteristics, fetal biometry, and laboratory examination, all of these parameters are easy to access. However, our study is limited by the availability of single center data and retrospective study and there was a certain degree of bias in the study because of the quality of medical records.
Herein, the prediction models displayed by nomograms are supposed to be clinically handy and simple tools for predicting intrapartum cesarean section. These nomograms can provide an individualized assessment and consultation under the New Labor Standard by using easily identifiable demographic and biometric data, particularly for those without specific maternal or fetal indications but requiring cesarean section. For women at a high risk of intrapartum cesarean section, the potential risks involved in pursuing a vaginal delivery versus an elective cesarean section should be provided to allow them to make informed choices before the trial of labor. Moreover, during the labor process, this risk assessment tool can help clinicians better monitor the labor process and decide whether or not to continue the trial labor or transfer to the cesarean section in time. Meanwhile, as for the low-risk population, this model reassures most women regarding their likely success at having an uncomplicated vaginal delivery and encourages them to pursue vaginal labor.