Table 3.

Studies investigating GDM neonatal microbiome.

References	Patients	Specimens	Technique	Results	Clinical significance
Wang et al. (103)	486 pregnant Chinese women and neonates (GDM and controls)	581 maternal (oral, intestinal and vaginal) and 248 neonatal (oral, pharyngeal, meconium and amniotic fluid) samples	16S rRNA gene and metagenomic sequencing	Pregnant women and neonates microbiota was remarkably altered in GDM Microbial variation concordance between mothers and neonates suffering from GDM	GDM can alter the microbiota of both pregnant women and neonates at birth, showing another form of inheritance and highlighting new prospect for intervention.
Ponzo et al. (104)	29 GDM infants	GDM neonatal fecal samples	16S rRNA gene sequencing	Significantly lower α-diversity in the GDM offspring's microbiota than the corresponding mothers but few Bacteroides and Blautia oligotypes were shared. GDM infants showed higher relative abundance of proinflammatory taxa, a low complexity and a high inter-individual variability. Earlier maternal nutritional habits were more strongly associated with the offspring microbiota. Separation of the infant microbiota according to the type of feeding (breastfeeding vs. formula-feeding).	Many maternal conditions impact on the microbiota composition of GDM offspring whose microbiota showed increased abundance of pro-inflammatory taxa.
Hu et al. (105)	23 newborns stratified by maternal diabetes status (4 pre-gestational type 2 DM, including one mother with dizygotic twins, 5 GDM) and 13 controls	Meconium samples	16S rRNA sequencing, taxonomy assignment and diversity computation	The bacterial content significantly differed by maternal diabetes status, with ↑ alpha diversity of the pre-gestational type 2 DM group than that of no-diabetes or GDM group. No global difference was found between babies delivered vaginally vs. via Cesarean-section.	Meconium microbiome of infants born to mothers with the pre-gestational type 2 DM is enriched for the same bacterial taxa as those reported in the fecal microbiome of adult DM patients. The most robust predictor for the meconium microbiota composition was the maternal diabetes status that preceded pregnancy
Lowe et al. (90)	34 full-term and C-sectioned newborns (20 GDM: 15 GDM grade A1 and 5 GDM grade A2 and 14 controls)	Meconium samples	16S rRNA gene sequencing and bionformatics	↓ alpha-diversity, ↑ Proteobacteria. and Actinobacteria and ↓ Bacteroidetes in GDM newborns. Several phyla found in controls were absent in GDM newborns. Bacteria in GDM_A2 newborns did not show variation compared to controls, which might be attributed to the additional intervention by insulin.	There are important implications for the GDM's effects on the gut microbiota of newborns with possible consequences even later in life.
Shokry et al. (84)	418 pregnant women/neonates (147 GDM and 271 controls) neonates	Meconium samples	16S rRNA gene sequencing	Microbial communities were significantly altered in neonates from the GDM mothers with a ↓ alpha-diversity and in the abundance of Firmicutes and Proteobacteria.	GDM impacts the neonatal meconium microbiota

GDM, gestational diabetes mellitus; DM, diebetes mellitus. ↑ represents an increase and ↓ represents a decrease.