We observed a similar gut microbiota composition of post-partum women stratified by previous or not GDM or type of delivery. Also, we did not detect a difference in the overall composition of the infant’s microbiota according to previous GDM or type of delivery. Considering the relative abundance, the Victivallis genus was higher in postpartum women who had a natural delivery. Besides, the analysis of the microbiota of offspring with exclusive breastfeeding showed a higher relative abundance of genus Bacteroides and Staphylococcus, which might be compatible with an ecological succession of the intestinal bacterial content.
The lack of difference when women who had or not GDM and their offspring were compared is similar to results obtained by other investigators. Hasan et al.(30)evaluated 60 women who had GDM and 65 control and their offspring five years post-partum and found no significant differences observed in microbiota composition between the two groups and their offspring; mother and her child have a more similar microbiota composition when compared to unrelated children, other mothers, or the children compared to each other.
In another study of pregnant women, fecal samples were collected from 74 women with GDM and 73 healthy pregnancies, as well as meconium, oral, pharyngeal, and amniotic fluid from their neonates; no difference was found in either intestinal or vaginal microbiota(6). However, this study was able to show that some genera could be related to hyperglycemia, they found that low intestinal Faecalibacterium/Fusobacterium ratios corresponded to high blood glucose values in mothers. Genera such as Prevotella, Streptococcus, Bacteroides, and Lactobacillus were prevalent in samples from several maternal and neonatal microbiome sites, suggesting GDM response generations' role.
It is important to mention a limitation of those studies whose analyses were not controlled for body adiposity. It is well known that GDM is accompanied by excess weight that can per se modify the microbiota composition(31). Our study had the advantage of including weight-matched participants in the groups, allowing us to attribute differences found in microbiota profiles to the GDM. Before pregnancy, they were overweight or obese and maintained their nutritional status until the postpartum period. In this context, a study analyzed the microbiota of infants from overweight and normal-weight mothers and possible relations with normal or excessive weight gain during pregnancy(32). Elevated pre-pregnancy maternal BMI was associated with higher abundances of Bacteroides, Clostridium, and Staphylococcus and lower concentrations of the Bifidobacterium group in infant’s microbiota. Lactobacillus, Flavonifractor, Erysipelotrichaceae, and Gammaproteobacteria were reduced in neonates from mothers with GDM after adjusting for pre-pregnancy BMI, reinforcing an independent role of maternal GDM in the infant microbial composition [10]. As far as relative abundances are concerned, we detected several correlations of bacterial taxa with clinical and laboratory data. Our findings add and corroborate those reported in the literature (Supplementary material, Table 1S).
The overall composition of the gut microbiota did not differ according to delivery type, but the relative abundance of Victivallis was associated with natural delivery. Victivallis is a Gram-negative, coccus-shaped bacteria found in the human digestive tract and is strictly anaerobic. An experimental study in obese rats showed that those with a richer abundance of some genera of bacteria, among them Victivallis together with Barnesiella, Bilophila, Butyricimonas, Clostridium XIVa, Akkermansia, Raoultella, and Blautia, presented a better response to non-drug therapy for weight loss(33). Furthermore, a randomized clinical study in humans showed that the group that received prebiotic fibers improved the metabolic parameters of glycemia and lipids, together with an increase in bacterial genera such as Akkermansia, Ruminococcus_2, Victivallis, and Comamonas(34). Thus, we propose that the microbiome in natural birth may contain composition characteristics associated with potential benefits in metabolism and weight loss.
We did not detect a difference in the overall composition of the infant’s microbiota according to previous GDM or type of delivery. It is important to consider an age variation among the infants and that intestinal colonization is highly dependent on exposures in their first two years of life(35). Reports on the microbiota of women who had GDM, and their offspring are controversial. A study compared the 29 GDM offspring to 19 normoglycemic-mother offspring with fecal samples collected during the first week of life(36). Some Bacteroides and Blautia oligotypes were shared by the GDM mothers and their offspring, suggesting maternal microbial imprinting. Interestingly, these infants from GDM mothers showed a higher relative abundance of proinflammatory bacteria than infants from healthy women. Another study suggested that GDM could be associated with decreased microbiota richness in the newborns when the meconium DNA from 34 full-term and c-sectioned newborns, in which 20 newborns had mothers diagnosed with GDM, were compared(37). In another comparison of meconium of 23 newborns from 9 mothers with DM or GDM, and 13 from healthy mothers, the microbiota of the GDM and healthy groups showed lower alpha diversity than that of the DM group(12). No difference was found between babies delivered vaginally versus via Cesarean-section, in the same line as our results.
Our findings evidenced the impact of breastfeeding in the offspring microbiota. Babies exclusively breastfed showed a greater abundance of Bacteroides and Staphylococcus. Since Bacteroides is one of the most frequent genera in the stable microbiome, we interpreted that could indicate an ecological progression of intestinal flora. The intestinal microbiome develops until the first two years of life, considered a window of opportunity for microbial modulation(38). Similar to our results, Bacteroides and Bifidobacterium were more abundant in 40-day aged infants exclusively breastfed compared to formula-fed ones(39). Bacteroides have been associated with beneficial effects in the earlier neonatal phase. Breast milk factors, like human milk oligosaccharides (HMO), favors Bacteroides colonization which is important in activating immunologic functions. This genus and others commensal bacteria stimulate lymphoid elements and enhance intestinal epithelium (microvilli and tight junctions). These also activate the release of mucin by goblet epithelial cells, forming a glycocalyx that breaks down a physical and antibacterial barrier(40). In an experimental study, germ-free mice colonized with Bacteroides thetaiodamicron activated epithelial genes, such as upregulation of polymeric IgA, involved in the barrier function (41). Staphylococcus genus was already described in association with breastfeeding. Comparing fecal microbiota of breast-fed and formula-fed infants, families Staphylococcaceae and Pasteurellaceae were only found in the breast-fed infant microbiome(42). The intestine and microbiota maturation undergo a process of colonization primarily by aerobic bacteria and open opportunity for the installation of anaerobes that constitute the main profile of the stable intestinal microbiota in adulthood(43). We believe that breastfeeding contributes favorably to the process of ecological succession in forming the gut microbiota and contributing to a better immune function.
There is plenty of evidence indicating that feeding type is relevant for early microbial colonization. Breast milk is prebiotic and probiotic in nature, contains HMO and bacteria, and influences infant gut microbiota composition indirectly (transfer of prebiotics) and directly (vertical transmission of bacteria), providing pioneering species. In contrast, formula-fed infants are exposed to different carbohydrates, bacteria, and nutrients, causing different microbial colonization patterns. It has consistently reported that breastfed infants’ stools than compared to formula-feds ones contain higher levels of Bifidobacterium and Lactobacillus and lower levels of potential pathogens than those infants with formula-fed(44).
The proposition that gut microbiota's acquisition begins intrauterine was contested, and studies have supported that colonization begins at birth (45)(46)(47). Relevant roles in the colonization are played by the delivery type, nutrition procedures and antibiotics use(48),(49),(50). The relevance of the former factors was shown in an analysis of the intestinal microbiome of 120 babies six weeks after delivery; the microbiome of cesarean-born babies differed from vaginally delivered ones, but this difference was partially restored by exclusive breastfeeding (51).
Our study has limitations and strengths. As all participants had excess weight, we could not test whether obesity confers additional impact in the microbiota composition beyond GDM. Infants were very young, so their intestinal flora is not well established. On the other hand, the longitudinal design and long follow-up of women during pregnancy and the puerperium, and the early evaluation of their babies, allowed us to think about the hypothesis of ecological succession in forming the gut microbiota.