Background Women at high risk of prenatal depressive symptomology have higher rates of adverse obstetric outcomes (1) and altered infant development (2). The mechanisms underpinning this may be linked to inappropriate remodelling of the microbiome during pregnancy and subsequent vertical transmission of a suboptimal microbiome at birth.

Aim This cross-sectional study aimed to assess the association between the maternal microbiome and depressive symptoms.

Method Women enrolled in the IMPROvED study at Cork University Maternity Hospital (3) completed the Edinburgh Postnatal Depression Scale (EPDS) and provided faecal samples during the second (n=46) and third trimester (n=33) of pregnancy. Vaginal swabs were collected prior to delivery (n=60). EPDS ≤8 and EPDS ≥9 were used to indicate low and high depressive symptoms respectively. Microbial community structure analysed by 16S rRNA gene sequencing.

Results Women reporting higher depressive symptoms in second trimester had reduced phylogenetic diversity (p=0.024) and species richness (chao1; p=0.040) of the gut microbiota. There were significant alterations observed at Phyla, Family and Genus level including an increase in the dominant Faecalibacterium (p=0.029) among the higher depressive group. The magnitude of the depression-associated gut alterations was greatly reduced in the third trimester. The vaginal microbiome remained largely unchanged by prenatal depressive symptoms.

Conclusions The experience of depressive symptoms in mid pregnancy is associated with marked alterations in the maternal gut microbiome that do not persist into late pregnancy. Further studies are planned to clarify the implications of these depression-associated maternal microbiome alterations during pregnancy for obstetric outcomes and infant development.