Strengths and Limitations
The strengths of our study include the following: (1) this study is a prospective longitudinal study that measured ultrasound parameters of the fetal head station and position throughout the first and second labor stages in women with singleton pregnancies at term. (2) In this double-blinded study, the researchers and the managing clinicians were both blinded to the respective findings to avoid potential bias. (3) New objective and simple models based on the ultrasound parameters and clinical variables were shown to predict the internal fetal head rotation and delivery mode. However, we do acknowledge some limitations. Firstly, our study population included only Chinese women, and our results might not be representative of other ethnic populations. Secondly, neonatal birth weight is also a significant risk factor according to the mode of delivery in our observational study; however, we did not introduce this item as a predictive factor because of lacking a precise method to estimate the fetal weight before delivery. Furthermore, we should carry out the external validation of the prediction model.