Interpretation
The reason why we comprehensively took all above factors into account to build the model was that the predictive performance of single cervical measurement is not satisfied.16, 25, 26 The mechanism of PTB in twin maternity is subjected to various mechanical stimuli (two continuously growing foetuses and the expanding uterus) and biochemical stimuli (inflammatory factors, fetoplacental signals and steroid hormones).35, 36 There seem to be structure-function associations between SPTB and cervical microstructure, geometry, and mechanical function, which are not fully understood.37Recently, researchers proposed a new conceptual framework for the theory of PTB in which a maternal clinical phenotype potentially related to a certain perinatal outcome is characterized by a series of common clinical characteristics observed during pregnancy.27, 38 Demographic factors such as age, race, BMI, history of PTB, previous uterine surgeries, smoking, and prevalence of PTB in that specific area may indicate the initial states and variations in the cervix, including geometry and mechanical function, which increase the risk of cervical insufficiency. All these risk factors have their interconnected effects and a computational framework in changing and remodelling the cervix.39-42
However, it has been argued that maternal factors or cervix geometry (including length) alone do not perform well in PTB risk assessment, primarily due to poor sensitivity.16, 25, 26, 43 In our study, we specifically investigated the role of cervical measurement data and maternal demographic characteristics on SPTB probability at < 32 weeks. By doing so, we have found that nulliparity, monochorionicity, lower prepregnancy BMI, previous preterm birth or late abortion, cervical funneling and shorter cervical length confers an increased risk of PTB at <32 weeks and then build the nomogram.
By our predition model, clinicians can counsel the patients and define the follow-up schedule according to a patient’s individual risk of PTB. Thus, the ability to identify patients at higher risk for SPTB will assist us to schedule tighter follow-ups or administer targeted interventions such as antenatal corticosteroid administration, tocolytic therapy and transfer to a tertiary medical centre and reduce overtreatment to those at lower risk. Further clinical trials are warranted to validate and improve its diagnostic performance, and the corresponding online calculator can be updated and serve as a basic screening tool for clinical practice and subsequent research.