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Borrego-Ruiz et al. Microbiome Res Rep. 2025;4:20 https://dx.doi.org/10.20517/mrr.2024.78 Page 3 of 22

microbiomes [20,21] . Interestingly, the maternal transfer of bacteria to the fetus plays a significant role in the
establishment of a healthy neonatal microbiome, which may subsequently influence both the immune
[22]
[23]
system maturation and the neurodevelopment . The maternal gut microbiota during late pregnancy is
decreased in microbial α-diversity compared to the first trimester, with a decline in the abundance of
members of Bacillota but an elevation in the bacteria belonging to the phyla Pseudomonadota and
Actinomycetota, as well as to the Streptococcus genus [24,25] . Furthermore, the administration of probiotics,
prebiotics, or synbiotics to the mother during pregnancy has a significant influence on fetal and neonatal
GM [17,26] . Table 1 shows studies conducted on the effects of probiotic and prebiotic supplementation during
pregnancy and early life, and their influence on the composition and diversity of the infant’s GM [27-47] .

In several studies on probiotic supplementation during pregnancy and infancy, diverse effects on GM
composition and immune development have been reported. Rinne et al. evaluated the effects of
Lacticaseibacillus rhamnosus (L. rhamnosus) strain GG on infant gut microbiota and immune markers in a
[32]
study of 96 infants whose mothers received either a probiotic or placebo before delivery, and infants
continued the assigned treatment postnatally . At 6 months, breastfed infants supplemented with
[27]
probiotics showed higher counts of Bifidobacterium and Lactobacillus/Enterococcus. Additionally, probiotic-
supplemented infants exhibited increased IgG-secreting cells at 3 months and higher IgM, IgA, and IgG-cell
counts at 12 months compared to the placebo group, which suggests that probiotics administered during
breastfeeding may positively influence gut immunity. Gueimonde et al. examined maternal
supplementation with L. rhamnosus strain GG from 2-4 weeks before delivery until 3 weeks postpartum in
82 infants . At 5 days of age, infants in the probiotic group showed higher colonization of Bifidobacterium
[28]
breve (B. breve), but this effect did not persist at 3 weeks. These authors concluded that the transfer and
initial establishment of bifidobacteria in neonates result from maternal consumption of L. rhamnosus strain
GG. Rinne et al. studied 132 newborns whose mothers received either probiotics or placebo before and for 6
months postnatally . The probiotic treatment did not significantly alter overall gut microbiota
[29]
composition, but at 6 months, infants in the probiotic group had higher clostridia levels compared to
placebo, indicating its role in microbiota succession. Grönlund et al. studied the colonization of
Bifidobacterium species in 61 mother-infant pairs, with mothers receiving probiotics from 30-35 weeks of
[30]
gestation . Only infants of allergic mothers were colonized with Bifidobacterium adolescentis
(B. adolescentis), and their mothers had significantly lower bifidobacterial levels in milk. Consequently, the
presence of bacteria in breast milk should be recognized as a key contributor to the development of the
intestinal microbiota in infants. Kukkonen et al. tested a combination of probiotics and prebiotics in 1,223
pregnant women, showing that probiotic-supplemented infants had higher colonization by lactobacilli and
Propionibacterium at 3 and 6 months, although the intervention did not reduce allergic disease incidence by
age 2 years . Building on these findings, the authors posit an inverse correlation between atopic diseases
[31]
and gut colonization by probiotics. Abrahamsson et al. assessed the effects of Limosilactobacillus reuteri
(L. reuteri) supplementation, finding that at 5 days, the probiotic group had significantly higher
colonization, but prevalence declined over time . However, the probiotic L. reuteri was found in breast
milk in nearly all infants following oral supplementation during the first year of life, and in some infants
who were not treated. Niers et al. evaluated a mixture of probiotics administered prenatally to mothers of
high-risk children, showing a preventive effect on eczema that persisted until age 2 . This preventive effect,
[33]
related to probiotics, appears to be established within the first 3 months of life. Grönlund et al. applied two
probiotic combinations in 61 mother-infant pairs, finding significant effects on maternal-infant
[34]
Bifidobacterium counts, but no impact on colonization frequencies . The authors concluded that maternal
colonization by Bifidobacterium bifidum (B. bifidum) had the most consistent effects on the infant’s
bifidobacterial microbiota. Conversely, maternal probiotic treatment had minimal impact on the
aforementioned mother-infant association. Grześkowiak et al. used two probiotic combinations in 57
mother-infant pairs, showing significant differences in Lactobacillus-Enterococcus counts, but no major