Prognostic model on niche development after a first caesarean section: development and internal validation.

• This is the first prediction model for development of a niche, including important surgical factors, in a population with a first elective or emergency CS. • More attention should be paid to surgical factors (double-layer closure, less surgical experience, other suture material than Vicryl) given their effect on niche development. • Different factors contribute to development of a niche compared to development of a large niche. • This prediction model is, unfortunately, not usable in clinical practice due to lack of discriminative ability and accuracy. • Proper suturing and correct approximation rather than single- versus double-layer uterine closure could play an important role and needs attention during training of residents. • Clinicians should be aware that suture material influences niche development. To develop and internally validate a prognostic prediction model for development of a niche in the uterine scar after a first caesarean section (CS). Secondary analyses on data of a randomized controlled trial, performed in 32 hospitals in the Netherlands among women undergoing a first caesarean section. We used multivariable backward logistic regression. Missing data were handled using multiple imputation. Model performance was assessed by calibration and discrimination. Internal validation using bootstrapping techniques took place. The outcome was 'development of a niche in the uterus', defined as an indentation of ≥ 2 mm in the myometrium. We developed two models to predict niche development: in the total population and after elective CS. Patient related risk factors were: gestational age, twin pregnancy and smoking, and surgery related risk factors were double-layer closure and less surgical experience. Multiparity and Vicryl suture material were protective factors. The prediction model in women undergoing elective CS revealed similar results. After internal validation, Nagelkerke R2 ranged from 0.01 to 0.05 and was considered low; median area under the curve (AUC) ranged from 0.56 to 0.62, indicating failed to poor discriminative ability. The model cannot be used to accurately predict the development of a niche after a first CS. However, several factors seem to influence scar healing which indicates possibilities for future prevention such as surgical experience and suture material. The search for additional risk factors that play a role in development of a niche should be continued to improve the discriminative ability. [ABSTRACT FROM AUTHOR]