Prebiotics During Pregnancy Could Cut Baby’s Allergy Risk From Labour Antibiotics by 5x

If you or someone close to you has a child with eczema or food allergies, there is a reasonable chance antibiotics played a role during birth, and new research from Western Australia suggests the window to intervene may open months before labour even begins. A randomised controlled trial published in the journal Allergy found that mothers who took daily prebiotic supplements during pregnancy and breastfeeding appeared to protect their babies from the steep allergy risks associated with intrapartum antibiotics (antibiotics given during labour). The effect sizes are striking enough to matter clinically, even though the researchers are careful to describe the analysis as exploratory.

Key takeaways:

• Among mothers who did not take prebiotics, antibiotics given during labour were linked to a 6.42-times higher risk of infant eczema, a 5.67-times higher risk of IgE-mediated food allergy, and a 3.56-times higher risk of allergen sensitisation.
• In mothers who took GOS/FOS prebiotics, those elevated risks were not observed.
• The prebiotic used was a combination of galacto-oligosaccharides (GOS) and fructo-oligosaccharides (FOS), started at 18-20 weeks of pregnancy.
• This is exploratory research: the finding needs replication before it can change clinical practice.

Intrapartum antibiotics raised infant allergy risk dramatically without prebiotics

The headline finding from the SYMBA trial, run by researchers at The Kids Research Institute Australia in Western Australia, is that intrapartum antibiotic exposure was strongly associated with infant allergic disease, but only in mothers who were not taking prebiotics. Among the 568 pregnant women enrolled, roughly 21% of infants also received antibiotics at some point during the trial period. When researchers isolated the intrapartum phase specifically, the numbers were stark: babies born to mothers who received antibiotics during labour but no prebiotics faced a 5.67-fold increase in IgE-mediated food allergy risk (IgE, or immunoglobulin E, is the antibody most associated with classic allergic reactions like peanut anaphylaxis) and a 6.42-fold increase in medically diagnosed atopic eczema. Allergen sensitisation, meaning a measurable immune response to a potential allergen even without full symptoms, was 3.56 times more likely. In the prebiotic group, none of these associations reached statistical significance.

Lead researcher Summer Walker described the stakes plainly: "Among mothers who did not take prebiotics, antibiotic exposure during labour was associated with a more than five-fold increase in food allergy risk in babies."

Why labour is the most vulnerable window for a baby's immune programming

The timing matters because of how antibiotic levels behave around birth. Antibiotics reach bactericidal concentrations in the umbilical cord within 30 minutes of maternal administration and remain active there for several hours, regardless of how long labour lasts. That means even a single dose of Group B strep prophylaxis, one of the most common reasons for intrapartum antibiotics, exposes the newborn gut to significant antibiotic pressure right at the moment it is being seeded with the mother's microbiome.

Food allergy now affects roughly 8% of children globally, a figure that has climbed steadily over recent decades, and disruption of the early gut microbiome is one of the most studied candidate explanations. For parents managing a child with IgE-mediated food allergy, eczema, or multiple sensitisations, the idea that birth-time antibiotic exposure may have set an immune trajectory is not abstract. Walker put it directly: "Our findings suggest a particularly vulnerable period around birth where antibiotic use may negatively influence a baby's developing immune system."

The mechanism the researchers point to involves short-chain fatty acids (SCFAs), small molecules produced when gut bacteria ferment dietary fibre. SCFAs can cross the placental barrier and appear to modulate fetal immune development. When antibiotics reduce maternal gut microbial diversity, SCFA production drops, and with it a key signal telling the developing immune system to tolerate rather than attack common environmental proteins.

How the SYMBA trial was designed and what it measured

The SYMBA trial enrolled 568 pregnant women at elevated risk of having an allergic baby, defined by a family history of allergic disease. Many participants came from the ORIGINS longitudinal birth cohort in Western Australia, which has tracked child health outcomes since birth. Mothers were randomly assigned to take either a daily prebiotic powder containing GOS and FOS (galacto-oligosaccharides and fructo-oligosaccharides, two types of non-digestible carbohydrates that selectively feed beneficial gut bacteria) or a matched maltodextrin placebo, starting at 18-20 weeks of pregnancy and continuing through six months of breastfeeding.

Antibiotic use was recorded monthly and sorted into four phases: before birth, during labour, at caesarean section, and during lactation. Only intrapartum antibiotics showed a significant interaction with prebiotic status. Antibiotics at the other three phases were not significantly linked to infant allergic outcomes, suggesting the labour window is distinctly sensitive. Infant allergic outcomes, including allergen skin-prick sensitisation, IgE-mediated food allergy, and medically diagnosed eczema, were assessed by one year of age.

A companion analysis found that the same GOS/FOS prebiotic combination increased beneficial Bifidobacterium in both maternal and infant gut microbiomes while reducing less desirable bacterial groups, suggesting a plausible biological pathway from supplement to immune outcome. Early dominance of Bifidobacterium in the infant gut is consistently associated with immune tolerance and lower allergy risk in the first year of life.

What this could mean if you are pregnant or planning to be

This is exploratory research, which means it should inform a conversation with your midwife or obstetrician rather than prompt a solo trip to the supplement aisle. That said, GOS/FOS prebiotics are considered safe in pregnancy, and if you already know you are Group B strep positive (meaning intrapartum antibiotics are likely), this finding gives you something specific to raise with your care team.

The analysis also helps explain a puzzling result from the original SYMBA trial: when all participants were analysed together, maternal prebiotics did not show an overall reduction in infant allergic disease. The interaction analysis suggests that prebiotics may have had a real effect, but only in the subgroup that needed them most, specifically those exposed to intrapartum antibiotics. That kind of subgroup finding can easily disappear in a pooled analysis.

For families already dealing with infant eczema or food allergy, this research does not offer a retroactive fix. What it does is clarify a specific exposure that may have mattered, and point toward a potential protective strategy for future pregnancies.

Open questions about prebiotic timing, dose, and replication

The researchers are explicit that this analysis is exploratory and that the trial was not originally powered to detect this specific interaction. As a systematic review of prebiotics in infant allergy prevention notes, optimal strain, dose, duration, and timing for prebiotic interventions remain unclear, and this study does not resolve those questions. Future trials designed specifically around the intrapartum antibiotic interaction, with larger sample sizes and pre-specified subgroup analyses, will be needed before this becomes a clinical recommendation.

What the SYMBA trial does establish is a signal worth following: the combination of intrapartum antibiotic exposure and absence of prebiotic supplementation may create a particularly adverse immune-programming environment in the newborn, and that combination may be modifiable.

Common Questions

Which prebiotics were used in the study? The supplement was a combination of galacto-oligosaccharides (GOS) and fructo-oligosaccharides (FOS), taken as a daily powder from around 18-20 weeks of pregnancy until six months after birth.

Does this mean pregnant women should start taking prebiotics before labour? Not as a formal recommendation yet. The analysis is described as exploratory and needs replication in larger, specifically designed trials. If you are likely to receive antibiotics during labour, such as for Group B strep, it is worth discussing prebiotic supplementation with your doctor or midwife.

Did prebiotics prevent all infant allergies? No. The protective association was specific to babies whose mothers received antibiotics during labour. Prebiotics did not show a significant overall reduction in allergic disease when all participants were analysed together.

Are intrapartum antibiotics avoidable? Often they are clinically necessary and potentially life-saving, particularly for preventing Group B streptococcal infection in the newborn. The study's point is not to avoid antibiotics but to explore whether prebiotics can offset their downstream immune effects.

References

1. Summer Walker, et al. (2026). Maternal Prebiotic Supplementation Modifies Associations Between Intrapartum Antibiotics and Infant Allergy. Allergy. https://doi.org/10.1111/all.70450
2. (2026). Maternal prebiotics may reduce infant allergy linked to antibiotic use in labour: Aussie study. https://www.ausdoc.com.au/news/maternal-prebiotics-may-reduce-infant-allergy-linked-to-antibiotic-use-in-labour-aussie-study/
3. Debra J. Palmer, Alana R. Cuthbert, Thomas R. Sullivan, et al. (2025). Effects of pregnancy and lactation prebiotics supplementation on infant allergic disease: A randomized controlled trial. Journal of Allergy and Clinical Immunology. https://doi.org/10.1016/j.jaci.2024.08.009
4. Margherita Di Costanzo, Adriana Vella, Claudia Infantino, et al. (2024). Probiotics in Infancy and Childhood for Food Allergy Prevention and Treatment. Nutrients. https://doi.org/10.3390/nu16020297
5. Jacquelyn M. Jones, Stacey N. Reinke, Mahsa Mousavi-Derazmahalleh, et al. (2024). Maternal prebiotic supplementation during pregnancy and lactation modifies the microbiome and short chain fatty acid profile of both mother and infant. Clinical Nutrition. https://doi.org/10.1016/j.clnu.2024.02.030
6. Bożena Cukrowska, Joanna B. Bierła, Magdalena Zakrzewska, Mark Klukowski, Elżbieta Maciorkowska (2020). The Relationship between the Infant Gut Microbiota and Allergy. The Role of Bifidobacterium breve and Prebiotic Oligosaccharides in the Activation of Anti-Allergic Mechanisms in Early Life. Nutrients. https://doi.org/10.3390/nu12040946
7. The Role of Prebiotics and Probiotics in Prevention of Allergic Diseases in Infants – PMC. NIH. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7772719/