Study Design

We used a sequential explanatory mixed-methods research design, which offers unique advantages in adherence studies. Thus, we chose this design to increase the depth and scope of the study. In the first phase, we investigated the effects of relevant demographic and disease-related characteristics on FU adherence in bariatric patients using quantitative investigation. Subsequently, in the second phase, we explored personal, family, and social factors influencing FU adherence through semi-structured interviews.

Phase One—Data Source and Study Population

Patients were identified from the bariatric surgery database within the division of Gastrointestinal Surgery of the West China Hospital, which contains information regarding demographics, medical history, treatments, and FU records of patients who underwent bariatric surgery at the hospital since 2018. Demographic information includes sex, ethnicity, level of education, employment, home address, marital status, and history of drinking and smoking. The disease profile includes the duration of obesity, mental illness, obesity-related comorbidities, and medication history. Treatment information includes operative details and the length of the hospitalization. The FU information includes BMI, surgical outcomes, and remission of comorbidities, among other parameters. In the first year following surgery, four FU appointments were scheduled, including the 1st month, the 3rd month, the 6th month, and the 12th month. Adherence to FU was defined as attending 3 or 4 of these appointments, as established in a previous study [25]. The inclusion criteria for participants in this research were as follows: (a) individuals with Chinese nationality; (b) those who underwent RYGB or SG; (c) those who underwent surgery after January 2018; and (d) individuals with a minimum of one year elapsed since their surgery. Patients who had undergone revisional procedures were excluded. The database recorded 181 patients who were one-year post-surgery from January 2018 to December 2020. Ultimately, a total of 177 participants were enrolled after excluding two patients who underwent revisional procedures and two patients who couldn’t communicate in Mandarin.

Phase One—Data Collection and Analysis

Data were extracted from the register database. Demographic, disease, and treatment information were sourced from preoperative records. Patients were considered to have participated in FU appointments if they had a registration record and had completed the corresponding examinations (e.g., blood biochemistry, oral glucose tolerance test, etc.). Statistical analysis was performed using SPSS 25.0. Categorical variables were described as numbers and percentages. A P value of < 0.05 was considered statistically significant. Logistic regression models were used to examine the association between predictors and FU. To minimize the risk of overfitting the regression model, single-factor logistic regressions were used to select the predictors of FU. Finally, multiple-factor logistic regression was performed on the indicators that had demonstrated statistical significance in the previous single-factor logistic regression.

Phase Two

In the second phase, we performed descriptive research using semi-structured interviews. The second phase of this study aimed to further explore the individual, social, and family factors that affect the attendance of FU appointments after bariatric surgery, which were not captured in the first phase. The interview guide was developed and revised based on a literature review of bariatric surgery FU and a group discussion. The final interview guide included three questions: “What were the doctor’s recommendations regarding FU after bariatric surgery?” “Why did you not attend the FU visit?” “How did you manage the challenges you encountered after surgery?”.

Phase Two—Sampling and Recruitment

We employed purposive sampling strategies to select interviewees from among the participants in the quantitative study who exhibited low FU adherence. The sample size was based on data saturation, that is, no additional new themes or codes were identified during the interview [26]. After interviewing and analyzing data from 10 participants, the research team agreed that the codebook had reached saturation, and consequently, data collection was concluded. The first author (L.J.) and another investigator (Q.Y.) identified participants with low FU adherence from the Phase I quantitative study. Subsequently, these individuals were contacted to explain the study’s purpose and methodology and build rapport with them. Finally, participants with a strong willingness to communicate were invited to participate in the interview phase.

Phase Two -Data Collection and Analysis

Semi-structured interviews were conducted through the telephone at the participant’s preferred time. All interviews were conducted by the first author, a case manager with extensive experience in bariatric surgery management. No repeat interviews were conducted. All interviews were audio-recorded and transcribed verbatim. The mean duration of the interviews was 35 min.

A content analysis approach was used to analyze the qualitative data [27]. NVivo 11 (QSR International) software was used to encode all interview transcripts. After the interviews, two researchers independently listened to the recordings repeatedly and transcribed them within 24 h. The first author read the interview transcription in-depth, extracted the significant content, and then developed the initial codebook. Codes with similar content formed categories and related categories were organized into more comprehensive themes. The survey was conducted in Mandarin or Sichuan dialects. The quotes, codes, and themes were translated into English and back-translated by the investigator, who was skilled in Mandarin, Sichuan dialect, and English.

Integration of Data and Emergent Themes

First, qualitative and quantitative research results were presented separately, and then data were integrated into the discussion to fully understand the factors influencing patients’ adherence to FU appointments following bariatric surgery. We identified similarities and inconsistencies between the two studies and explored potential reasons for any differences observed. Our study prioritized qualitative results because they explained and complemented quantitative findings in depth [28].

Ethical Considerations

Ethics approval for the quantitative and qualitative studies was obtained from the Ethics Committee of the West China Hospital of Sichuan University (approval number: 2022506). Before starting the interview, participants gave electronic informed consent. Participants were allowed to refuse to answer any questions or withdraw from the study at any time, with no penalty incurred.