BACKGROUND: Understanding the link between pre-pregnancy nutritional status and gut microbiota during pregnancy may lead to novel maternal and child health interventions. We explored the association of pre-pregnancy body mass index (BMI) status with gut microbiota diversity and abundance during pregnancy. METHODS: A cross-sectional study was conducted on 90 pregnant women from primary health centers in Jakarta, Indonesia. Trained staff interviewed women on socio-demographic characteristics and nutrient intake, gathered data on pre-pregnancy BMI from antenatal records, and obtained fecal samples. Samples were analyzed for microbiota diversity indices [Shannon, Faith Phylogenetic Diversity (Faith PD), and Chao1] and abundance using 16S rRNA (ribosome ribonucleic acid) sequencing. Multivariate logistic regression was performed while adjusting for carbohydrate and protein intake, ethnicity, and education to determine the relationship between pre-pregnancy BMI and the alpha diversity index and the presence of the phylum Firmicutes and genera Prevotella and Blautia. RESULTS: Pregnant women who were overweight or obese (BMI ≥23.0 kg/m CONCLUSION: Pre-pregnancy overweight or obese status was associated with lower gut microbiota diversity and lower abundance of Firmicutes and Blautia among pregnant women in an urban community. These findings suggest that pre-pregnancy interventions to control body mass index may improve gut flora and potentially benefit pregnant women.