Diet is one of the strongest modulators of the gut microbiome, which is increasingly implicated in metabolic, immunological, and neurological programming in early life(1). To explore associations between diet, the microbiome, and health outcomes, stool samples are commonly collected from pregnant women participating in longitudinal birth cohorts. However, many cohorts recently established in Australia have recruited pregnant women who are highly educated (for example, (2)) and likely to be of higher socioeconomic status (SES)(3). The generalisability of research findings is limited when people living with socioeconomic disadvantage, who may benefit most from interventions and support, are underrepresented. Understanding the demographical differences between those interested and uninterested in participating in maternal microbiome studies may assist with devising recruitment strategies and/or eligibility criteria for future research. This study aimed to describe the sociodemographic and dietary characteristics of pregnant women who expressed interest in participating a gut microbiome study, compared to those who did not. Pregnant women aged ≥ 16 years were recruited to complete an online survey (estimated duration: 25-35 minutes; prize draw entry offered to win one of three AUD 200 vouchers) about food insecurity and diet via social media and flyers/posters at three public hospitals in South-East Queensland. The survey included the Household Food Security Survey Module and a food frequency questionnaire (FFQ). Dietary Guidelines Index 2013 criteria were applied to FFQ responses to obtain an overall diet quality score. At the end of the survey, participants indicated if they were interested in a related study about the gut microbiome. Of the 1,492 women who completed the survey, approximately half (n = 742, 49.7%) were interested in participating in a gut microbiome study. Those who expressed interest were more likely to be married or in a de facto relationship (odds ratio [OR]: 1.7, 95% confidence interval [CI]: 1.1-2.6, p = 0.009), to have a Bachelor degree or higher (OR: 1.3, 95% CI: 1.1-1.6, p = 0.007), to live in a high SES area (OR: 1.4, 95% CI: 1.1-1.7, p = 0.001), and in a food secure household (OR: 1.3, 95% CI: 1.0-1.6, p = 0.016). On average, diet quality scores were 2.7 points higher (95% CI: 1.3-4.0, p < 0.001) among those who expressed interest; this difference may be clinically important. These findings indicate that pregnant women interested in taking part in a gut microbiome study are likely to be more ‘advantaged’, with higher diet quality. More research is needed to improve understanding of barriers and enablers to participation in maternal microbiome research, particularly among those with lower SES. Additionally, to ensure pregnant women from a range of SES backgrounds are represented in microbiome research, a targeted effort is required to recruit pregnant women living with disadvantage in future studies.