Participant Personal Characteristics and Adherence to Oral Capsules: A Secondary Analysis of a Randomized Placebo-Controlled Trial of Antenatal Probiotics.

Background: Adherence to study interventions is critical to the conduct of randomized controlled trials (RCTs). The relationships between participant characteristics and intervention adherence are understudied in pregnant populations. The purpose of this study was to conduct a secondary analysis of adherence to study capsules in a double-masked, placebo-controlled RCT of a probiotic intervention to reduce antenatal Group B Streptococcus colonization, in relationship to participant characteristics.

Methods: We analyzed the relationship between capsule adherence rates and demographic characteristics among 81 RCT participants. Categorical variables were reported using counts and percentages, and continuous variables were expressed as means along with their standard deviations. For the univariate analyses, we compared demographic variables with adherence scores. A multivariate linear regression model was used to identify predictors of adherence.

Results: Average adherence was similar for control and probiotic group participants (P = .86) Univariate analysis showed that average adherence increased directly with age, education, and income. Participants who were partnered or living with others had higher average adherence compared with those who were single and living alone. Asian and White participants had the highest and Black participants had the lowest average, and there was no difference based on Hispanic ethnicity. Adjusting for all the variables in the regression, participants who identified as Black were significantly less likely to adhere to capsules than White participants, and those who were married or living with partners were more likely to adhere than the single participants.

Discussion: Diverse participants are critically important to RCTs. This secondary analysis provides evidence that participant characteristics and the social determinants of health play an important role in adherence to self-administered interventions in RCTs, although more research is needed. Our findings suggest that intentional consideration of RCT participant characteristics may allow for the development and tailoring of strategies to enhance intervention adherence. The study was registered on ClinicalTrials.gov (NCT03696953) on January 10, 2018.