Strengths and Limitations
To our knowledge, this is the first study to develop a predictive nomogram for PTB of twin gestations and a web-based calculator to improve the approachability of the prediction model. Our model could synthesize the most relevant risk factors for PTB, such as nulliparity, pre-pregnancy BMI, history of PTB or late abortion, chorionicity, cervical funneling and cervical length, and generate a risk percentage number for each patient, which had a predictive accuracy (AUC 0.856 [95% CI: 0.813-0.899]) significantly that was higher than that of either variable alone. The strengths of the study include the detailed, standardized data collection, high rate of follow-up and efficient statistical analysis. Based on the model, we could provide reliable risk estimation for clinical counselling, therapy decision-making, and follow-up strategies, rather than complicating the clinicians’ lives with close monitoring and administration resulting from an undefined or inherently subjective risk assessment. All data pertaining to characteristics in our study can be easily obtained in the obstetric units where the cervical assessment has been well standardized, and these data were obtained by well-trained specialists throughout the study period. Moreover, external validation and restricted cubic splines supported the test performance.
On the other hand, the present study has some limitations. Most importantly, our study is limited by its retrospective design. There is a possibility of confounding bias: patients with unmeasured or unobservable factors who were excluded may represent patients at higher risk. Second, the sample number of marginal risk scores is relatively insufficient, which limits generalizability because it might not fully reflect the actual situations of patients at the highest risk and who are may be the most clinically interesting population. Last, the study population in the two centres is limited to our own population (Asian). This potential limitation may also be considered as a strength. All women included in the study were followed up and treated only in the two tertiary medical centre, which limits confounding factors associated with the heterogeneity in provider bias, such as clinicians’ experience, and differences in process of monitoring and management for offering the intervention.