Could gut bacteria during pregnancy predict a baby's eczema risk?

Atopic dermatitis — eczema — is a condition that often leaves parents consumed by guilt. Now, a study has found that the composition of bacteria in a mother's gut during pregnancy can predict whether her baby will develop eczema within the first year of life, before the child is even born.

According to the journal Nature, a mother's gut microbiome is not only the primary source of bacteria that colonize a newborn's gut but is also linked to the baby's risk of developing atopic dermatitis.

Researchers Trishla Sinha and Alexandra Zhernakova at the University of Groningen and the University Medical Center Groningen in the Netherlands tracked 714 mother-infant pairs from the 12th week of pregnancy through the baby's first year of life. They analyzed 4,526 stool samples and cross-referenced the findings against 474 variables related to childbirth, breastfeeding, diet and health.

Mother's gut alone could predict baby's eczema risk

Mothers of babies diagnosed with atopic dermatitis within the first year of life had lower gut microbiome diversity than mothers of babies who did not develop the condition. Gut microbiome diversity measures both the number of bacterial species present and how evenly they are distributed.

The research team then tested whether stool samples collected from mothers at the time of delivery alone could predict whether their babies would develop eczema.

The model achieved an accuracy score of 0.74 — where 1.0 represents a perfect prediction and 0.5 is equivalent to a coin toss. While far from perfect, the result was reached without examining the babies at all.

Mothers with lower gut microbiome diversity were more likely to have been overweight before pregnancy or to have a history of smoking.

The research team said these findings had been measured for the first time and noted the need to verify whether the same results would hold in other studies.

Babies get their gut bacteria from their mothers

The research team traced the origins of bacteria living in infants' guts down to the genetic level.

Most previous research had treated bacteria with the same name in a mother and her baby as identical. This team went further, verifying whether same-named bacteria were genetically the same strain — because a shared bacterial species does not necessarily mean the baby's bacteria came directly from the mother.

Across 81 bacterial species, the team made 15,462 comparisons between mothers and their babies and found 7,345 instances of matching strains. The median proportion of bacteria that infants shared with their mothers was 33 percent, compared with a median of 0 percent when unrelated individuals were compared.

The more bacteria a mother harbored in her gut, the more likely those bacteria were to be passed to her baby, and strains transmitted from mother to infant at two weeks or one month after birth were far more likely to still be present at the baby's first birthday.

Breastfed babies shared more bacterial strains with their mothers than formula-fed babies did. However, breast milk appeared to work less as a direct channel for transferring bacteria and more as a medium that helped bacteria originating in the mother's gut establish themselves in the infant's digestive system.

The single biggest factor differentiating infants' gut microbiomes was whether they were born vaginally or by cesarean section, the research team said.

Babies born by cesarean section had fewer of the bacteria commonly found in vaginally delivered infants — particularly those involved in breaking down food. The gap was pronounced through the first three months of life and persisted beyond the first birthday.

Even among vaginal births, bacterial counts were lower in cases involving prolonged labor, epidural anesthesia, or a long interval between the rupture of membranes and delivery. The complexity and duration of the birth process, not just the delivery method, appeared to matter.

The research team noted a limitation: the participants were relatively healthy pregnant women from the northern Netherlands, so it remains unclear whether the same patterns would appear in high-risk pregnancies involving conditions such as preeclampsia or excessive gestational weight gain.

Reference

DOI: 10.1038/s41586-026-10922-9

Sinha, T., Brushett, S., Fernández-Pato, A. et al. Maternal influences on infant gut microbiome and health. Nature (2026).

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