Changes in the composition and function of the gut microbiome accompany type 1 diabetes in pregnancy

Background The gut microbiome changes in response to a range of external influences, life events and disease. Pregnancy is a natural life event involving major physiological adaptation but studies of the microbiome across pregnancy are scarce and findings inconsistent. Pregnancy in which the mother has type 1 diabetes (T1D) with disturbed glucose-insulin homeostasis increases maternal and fetal risks and knowledge of the gut microbiome in this context is lacking. To understand how T1D impacts the gut microbiome in pregnancy we used a combination of whole metagenomic sequencing (WMS) and 16S rRNA sequencing to define the composition and function of the gut bacterial microbiome across 145 pregnancies, 94 in women with T1D. Women were participants in the Environmental Determinants of Islet Autoimmunity (ENDIA) study, in which the child has a first-degree relative with T1D.Results Pregnant women with and without T1D exhibited taxonomic and functional changes in gut microbial composition across pregnancy. Profiles in women with T1D were distinct, with a decrease and increase, respectively, of bacteria with anti- and pro-inflammatory properties, and a decrease in bacteria that synthesize essential vitamins and metabolites. These changes were accentuated in trimester 3, often in opposite directions to women without T1D.Conclusions The gut microbiome changes in composition and function across pregnancy, but distinctly in women with T1D. The decrease in bacteria that produce anti-inflammatory mediators and essential B-group vitamins suggests that the gut microbiome may contribute to maternal and fetal complications in the T1D pregnancy, potentially opening new avenues for therapeutic intervention.