The newborn's microbiome: what is the impact of vaginal seeding?

Sensitivity to certain pathogens is often higher in infants born by caesarean section than in those born vaginally. For example, 64 to 82% of reported cases of methicillin-resistant Staphylococcus aureus (MRSA) skin infections in infants occurred in infants born by caesarean section [7].

Poor maternal transmission during caesarean birth may predispose infants to colonisation by pathogens. However, the clinical consequences of microbiome disruption in early life and pathogen carriage during this critical window of immune development remain to be determined [8]

We also know that the transmission of maternal gut bacteria begins during pregnancy [9], so boosting your own microbiome with prebiotics and probiotics can be an option to support your baby's microbiome.

Furthermore, a study examining the associations between mode of delivery and the diversity and colonisation patterns of the gut microbiota during the first year of life found that diversity and colonisation patterns were significantly associated with mode of delivery, though the long-term effect of these differences remains unknown. One study showed that the differences persisted for up to 6 months [10] only, whilst another study found differences lasting up to 4 years [11].

Aberrant microbial colonisation in infants has been associated with long-term effects on their metabolism, as the gut microbiome can contribute to obesity by increasing energy extraction or by altering metabolic signalling and inflammation [12]. In a study of 284 children born by caesarean section, researchers observed that at age 3, 15.7% of children born by caesarean section were obese, compared with 7.5% of children born vaginally [13]. 

Invariant natural killer T (iNKT) cells play a role in the pathogenesis of ulcerative colitis, a major form of inflammatory bowel disease, and in asthma. Microbial exposure early in life has lasting effects on these iNKT cells and, in their absence, subsequent exposure to factors that stimulate these cells can trigger an auto-inflammatory response [14]. This effect of the microbiome may explain the finding of a study showing a 20% increased risk of developing asthma in children born by caesarean section [15].
The risk of developing asthma [16] has also been associated with the type of bacteria contributing to the gut microbiota during the first 100 days of life. 

They also observe that infants born by caesarean section are more heavily colonised by Clostridium (associated with neonatal necrotising enterocolitis) during the first 3 weeks of life [17]. A healthy gut microbiota is considered to promote the development and maturation of the immune system, whereas an abnormal gut is considered the main cause of serious gastrointestinal infections during early childhood [18].

In one study, they observed that children with a parental history of asthma or allergies born by caesarean section presented a risk of atopy (i.e. a hypersensitivity to the environment that generally manifests as asthma, colds, or eczema) twice as high as those born vaginally. Birth by caesarean section was significantly associated with an increased likelihood of allergic rhinitis. The authors concluded that this may be explained by the lack of contact with the vaginal flora through caesarean section [19]. 

Please bear in mind, mama, that we are only talking about an increased risk here — this does not mean your child will not be healthy because you had a caesarean section! And caesarean sections are necessary for many of us, and it's a good thing they exist!

Furthermore, the microbiome of all infants born by caesarean section cannot be considered uniform, as some infants are born by caesarean section after the onset of labour or rupture of membranes, whilst others are born before the onset of labour or before rupture of membranes. Consequently, exposure to maternal vaginal bacteria will vary amongst all infants born by caesarean section. 

Finally, there are other ways to develop the microbiome, such as through breastfeeding or skin-to-skin contact!

The first step towards ensuring a healthy gut microbiome for your baby begins during the pregnancy. Maternal microbes are transferred for the first time in utero [20].

You can consume prebiotic fibres, which help contribute to the richness of the gut microbiome [21]. Consuming probiotics may also be beneficial [22]. These foods are also worth prioritising when introducing solid foods to your child, to support their healthy development!

Thebreastfeeding shapes the gut microbiome early in life, both directly through the infant's exposure to the milk microbiome and indirectly through factors in breast milk that affect bacterial growth and metabolism [23]. The benefits of breastfeeding are undeniable on the microbiome. 

Commensal bacteria present in breast milk and bacteria from the mother's areolar skin contribute to the early seeding of the infant's gut. A study showed that breastfeeding contributed 27.7% of bacteria from breast milk and 10.3% from areolar skin [24].

Skin-to-skin contact also helps support the development of the baby's microbiome [25].

Several studies have shown that owning a pet can in fact help increase the diversity of the gut microbiome. This finding is linked to the hygiene hypothesis, which suggests that limited exposure to infections early in life may actually be detrimental to the development of the immune system. One study in particular, involving 746 infants, found that owning a pet was associated with a greater abundance of two bacteria, Ruminococcus and Oscillospira. These bacteria have been associated with a lower risk of allergy and obesity in children [26].

A contact with the outside world will help children support their immune system. It may be worth letting children play outdoors, in the soil, to encourage the development of their defences and their microbiome.