Gestational diabetes and the human salivary microbiota: a longitudinal study during pregnancy and postpartum

Abstract

Background: An aberrant composition of the salivary microbiota has been found in individuals with type 2 diabetes, and in pregnant women salivary microbiota composition has been associated with preeclampsia and pre-term birth. Pregnant women, who develop gestational diabetes (GDM), have a high risk of developing type 2 diabetes after pregnancy. In the present study we assessed whether GDM is linked to variation in the oral microbial community by examining the diversity and composition of the salivary microbiota.

Method: In this observational study the salivary microbiota of pregnant women with GDM (n = 50) and normal glucose regulation (n = 160) in third trimester and 9 months postpartum was assessed by 16S rRNA gene amplicon sequencing of the V1-V3 region. GDM was diagnosed in accordance with the International Association of the Diabetes and Pregnancy Study Groups (IADPSG) criteria. Cross-sectional difference in alpha diversity was assessed using Student's t-test and longitudinal changes were assessed by mixed linear regression. Cross-sectional and longitudinal difference in beta diversity was assessed by permutational multivariate analyses of variance. Differentially abundant genera and OTUs were identified by negative binomial regression.

Results: In the third trimester, two species-level operational taxonomic units (OTUs), while eight OTUs postpartum were differentially abundant in women with GDM compared with normoglycaemic women. OTU richness, Shannon diversity and Pielou evenness decreased from late pregnancy to 9 months after delivery regardless of glycaemic status.

Conclusion: GDM is associated with a minor aberration of the salivary microbiota during late pregnancy and postpartum. For unknown reasons richness of the salivary microbiota decreased from late pregnancy to postpartum, which might be explained by the physiological changes of the immune system during human pregnancy.

Keywords: Bacterial species; Gestational diabetes mellitus; Gestational hyperglycaemia; Glycaemic traits; Pregnancy; Salivary microbiota.

Fig. 1

Alpha diversity of salivary microbiota during pregancy. Samples were rarefied to an equal sequencing depth of 10,000 reads and by observed OTUs (a), Shannon’s diversity (b) and Pielou’s evenness (c) alpha diversity in 3rd trimester of pregnancy in women with gestational diabetes (GDM; n = 50) and normoglycaemic women (n = 160) is presented. Boxes represent interquartile range (IQR), with the inside line representing the median. Values within 1.5 × IQR of the first and third quartiles are represented by whiskers. Circles represent individual samples with lines connecting samples from the same individual. Student’s t-test was used to test differences between normoglycaemic and GDM pregnancies

Fig. 2

Community structure in women with or without gestational diabetes. For all analyses samples were rarefied to an equal sequencing depth of 10,000 reads prior to principal coordinate (PCo) ordination based on weighted Unifrac distances. a Samples from pregnant women in the 3rd trimester with (n = 50) or without (n = 160) gestational diabetes. Points are individual samples and diamonds represent the average ordination scores and ellipses the 95% confidence intervals of a multivariate normal distribution of either group. R2 and P are from permutational multivariate analysis of variance (PERMANOVA). b Community structure in pregnant women with gestational diabetes diagnosed by fasting hyperglycaemia (n = 25) or stimulated hyperglycaemia (2 h after an oral glucose challenge; n = 8), respectively, or a combination of the two (n = 15). Configuration is similar to panel A. c The association between glycaemic traits and community structure during pregnancy regardless of GDM status as determined by PERMANOVA. Vectors representing direction and magnitude of each trait were fitted onto the 1st and 2nd PCo axes using the envfit function of the vegan R package. d Change in community structure from pregnancy to postpartum. Only samples from women examined at both time points are included (n = 43 and n = 81 for women with and without GDM respectively). R2 and P are from PERMANOVA testing for a difference in community structure between samples collected during the 3rd trimester and those collected postpartum and for a differential change in community structure in women with GDM compared to women without GDM

Fig. 3

Operational taxonomic units associated with gestational diabetes during the third trimester with and without adjustment for pre-pregnancy bodymass index. a Estimated log₂ fold difference in operational taxonomic unit (OTU) abundance between women with gestational diabetes (GDM, n = 50) and women with normal gestational glucose regulation (n = 160) during pregnancy and corresponding Benjamini-Hochberg adjusted P-values (Q) from the DESeq2 R package. Abundance is mean relative abundance of a given OTU. Prevalence is percentage of participants in which a given OTU is detected. Names of OTUs differentially abundant at a 10% false discovery rate are given at the lowest annotated taxonomic level. b Adjusted for pre-pregnancy body mass index in subset of women with available data (GDM, n = 43; normoglycaemic, n = 144)

Fig. 4

alpha diversity from third trimester of pregnancy to postpartum. Alpha diversity in pregnancy and postpartum as represented by observed richness (a), Shannon diversity (b) and Pielou evenness (c) based on samples from GDM (red, n = 43) and normoglycaemic (blue, n = 81) women with available faecal samples from 3rd trimester and 9 months postpartum. Samples were rarefied to an equal sequencing depth of 10,000 reads. Boxes represent interquartile range (IQR), with the inside line representing the median. Values within 1.5 × IQR of the first and third quartiles are represented by whiskers. Circles represent individual samples with lines connecting samples from the same individual. Students t-test were used to test differences between normoglycaemic and GDM pregnancies within each timepoint. Difference in richness, Shannon diversity and Pielou evenness between time points in GDM and normoglycaemic women combined was tested using a paired t-test