## 2 Materials and Methods
### The Conceptual Framework of a Cascading Delphi Method  
The framework proposed in this study was divided into five stages: preparation, Delphi-1 (risk identification), Delphi-2 (risk analysis), the calculation of S, O, and D (risk evaluation), and the compilation of a final report as presented in Figure 2. Each stage had several steps to complete the task. The conceptual framework of a cascading Delphi method approach to data collection for advanced surgical instrument, adapted from [PERSON] et al. [31], as shown in Figure 2.  
**Stage 1: Preparation:** to set the scene for the experts  
_Step 1. Choosing the device/instrument:_ a virtual prototype of flexible fetoscope and a clear description of the instrument were explained to the expert team. _Step 2. Building the FMEA expert team:_ the facilitator chose participants with prior experience and knowledge of the type of instrument being studied, and willingness to provide feedback. _Step 3. Meeting the FMEA expert team:_ the facilitator explained the objectives, FMEA, the process and their responsibilities to participating experts. **Stage 2: Delphi-1:** to identify the relevant failure modes (FMs)  
_Step 4. Analyzing the different parts and functions of the device/instrument online:_ the participants were presented with the figure of flexible fetoscope and an open-ended question (\"What are the new parts of the fetoscope, analyzed by function?\") during an individual online interview. Figure 2: Conceptual framework of a cascading Delphi method approach to data collection for advanced surgical instrument. _Step 5. Identifying potential failure modes (FMs) online:_ the experts were asked an open-ended question (\"What could possibly go wrong with which parts of the fetoscope in terms of the patients and fetuses?\") about the potential failure modes. Potential failure modes were listed. _Step 6. Preparing a summary of individual's comments:_ the facilitator summarized separately each interview with the experts. _Step 7. Sending the report to the individual expert concerned for review and amendment as required:_ the facilitator reduced the possibility of error or facilitator bias by sending each expert the summary of his/her own interview, for review and amendment as necessary. _Step 8. Preparing the Delphi-1 summary:_ the facilitator prepared a summary report on the views of all experts together. The outcomes of all experts are combined by the facilitator. Because of different wording of the same failure, some identified failure modes were merged to a single one, effectively avoiding overlap. Content analysis and generative AI (Claude) were applied to analyze qualitative data in this step. The generative AI (Claude) was used to generate new content of potential failure modes from all experts. **Stage 3: Delphi-2:** to analyze causes, effects, and detectability and provide scores for S, O, and D  
_Step 9. Analyzing potential failure causes, failure effects, detectability, and providing scores for each failure mode:_ the experts were asked open-ended questions to list the potential failure effects (\"What would the consequences be of a particular failure?\"), failure causes (\"Why would this failure occur?\"), and detectability (\"What is the potential to detect failures and intervene in time?\"). Two patient safety risk areas--namely, those concerning mother and fetus(es)--were considered when identifying failure effects. The experts provided input via email, and they were asked to score each potential failure mode for severity (S), probability of occurrence (O), and detectability (D). Each potential failure mode (FM) could be associated with more than one potential failure effect. Therefore, one failure mode could generate more than one potential failure cause (FC). To search for the root causes, each FC was taken into account to calculate a risk score. As in Table 1, the severity rating for the mother and surgeon is on a scale of 1-7, with 1 indicating no injuries and 7 indicating death.