Examining the relationship between maternal body size, gestational glucose tolerance status, mode of delivery and ethnicity on mother's milk microbiota at three months post-partum

Background: Breastfeeding provides a rich source of microbes that inoculate the infant's gastrointestinal tract (gut). It is unknown if and how maternal factors affect the microbial composition of mother's milk. We aimed to explore the associations between maternal body mass index (BMI), glucose tolerance status, mode of delivery and ethnicity and the microbial composition of mother's milk. Methods: Women were recruited during pregnancy and milk samples were collected at 3 months post-partum (ClinicalTrials.gov Identifier: NCT01405547). Demographic data, weight (self-reported), height and a 3-hour oral glucose tolerance test were conducted in late pregnancy (30 weeks gestation [95% CI 25-33 weeks]). Metagenomic DNA extraction and 16S ribosomal RNA (rRNA) gene sequencing of the V4 hypervariable region using an Illumina MiSeq platform was carried out on 113 milk samples.