Researchers studied whether pregnant women taking probiotics could improve their babies’ gut bacteria. They followed 26 mothers and newborns, giving some mothers a probiotic supplement (containing three helpful bacteria types) from week 32 of pregnancy until delivery, while others received nothing. By analyzing bacteria samples from mothers and babies at different time points, scientists discovered that probiotics did change which bacteria babies inherited from their mothers—specifically increasing bacteria from the placenta. However, these changes were temporary, and by 6 months, babies in both groups had similar gut bacteria. The study shows that what mothers pass to babies during birth is more complex than previously thought.

The Quick Take

  • What they studied: Whether pregnant women taking probiotic supplements (special beneficial bacteria) could change which bacteria their newborns inherited and improve baby gut health.
  • Who participated: 26 mother-baby pairs who had vaginal deliveries at full term. Mothers in the treatment group took probiotics from week 32 of pregnancy until birth; the other group took nothing.
  • Key finding: Prenatal probiotics temporarily changed which bacteria newborns received from their mothers—specifically increasing bacteria from the placenta—but these differences disappeared by 6 months of age.
  • What it means for you: While prenatal probiotics may slightly influence early baby gut bacteria, the long-term effects appear minimal. More research is needed before recommending probiotics to all pregnant women for this purpose. Talk to your doctor before taking any supplements during pregnancy.

The Research Details

This was a controlled study comparing two groups of pregnant women. One group took a probiotic supplement containing three types of beneficial bacteria (Bifidobacterium longum, Lactobacillus delbrueckii bulgaricus, and Streptococcus thermophilus) twice daily from week 32 of pregnancy until delivery. The other group received no supplement. Researchers collected bacteria samples from mothers’ intestines, vaginas, and placentas at delivery, and from babies’ intestines at days 1, 3, 14, and 6 months after birth. They used advanced genetic testing to identify which bacteria were present and where they came from.

The researchers used a special computer program called FEAST to track which maternal bacteria ended up in each baby’s gut. This allowed them to determine whether babies inherited more bacteria from their mother’s intestines, vagina, or placenta. They also measured how diverse the bacteria were and how stable the bacterial communities remained over time.

Understanding how babies get their first bacteria is important because these early microbes influence immune system development, digestion, and overall health. By tracking where bacteria come from, scientists can better understand if supplements actually change what babies inherit and whether those changes matter long-term.

This study was relatively small (26 mother-baby pairs), which limits how much we can generalize the findings. The study was registered in a clinical trial database, which is good for transparency. The researchers used modern genetic sequencing technology, which is reliable for identifying bacteria. However, the study was retrospectively registered (registered after it started), which is less ideal than registering before beginning. The findings show statistical significance for some measures but not others, suggesting some effects were stronger than others.

What the Results Show

Babies whose mothers took probiotics had different bacteria in their first stool samples compared to babies whose mothers didn’t take probiotics. Specifically, babies in the probiotic group had more bacteria that came from the placenta. The probiotic group also showed more stable bacterial communities in the first few days of life (days 1-3), meaning their bacteria changed less dramatically during this period.

However, these differences were temporary. By day 14 and especially by 6 months, babies in both groups had very similar bacteria. This suggests that while prenatal probiotics can influence which bacteria newborns initially receive, this effect doesn’t last long.

Interestingly, the study found that babies inherited most of their bacteria from their mother’s intestines, not from the vagina during delivery. The placenta also contributed bacteria, which was surprising to many researchers. The vagina contributed very little to babies’ initial bacteria, even though vaginal delivery is how babies are born.

The probiotic supplement reduced the amount of bacteria babies inherited from their mother’s intestines and vagina, but these reductions weren’t statistically significant (meaning they could have happened by chance). The study also showed that the source of bacteria changed over time—intestinal bacteria became more important as babies got older, while placental bacteria became less important.

Previous research suggested that babies mainly inherited bacteria during vaginal delivery, but this study found that the placenta and mother’s intestines are actually more important sources. This finding challenges earlier assumptions about how babies get colonized with bacteria. The temporary nature of probiotic effects aligns with some previous studies showing that probiotic benefits often don’t persist long-term.

The study was small with only 26 mother-baby pairs, making it harder to detect real differences or apply findings broadly. The study only included women with vaginal deliveries, so results may not apply to babies born by cesarean section. The probiotic supplement contained three specific bacteria strains, so results may not apply to other probiotic products. The study didn’t measure whether babies had better health outcomes—only whether their bacteria changed. Researchers didn’t track whether mothers actually took the supplements as prescribed.

The Bottom Line

Based on this research alone, prenatal probiotics are not yet recommended as a standard practice for improving baby gut health. The temporary nature of the effects and small study size mean we need more research. If you’re pregnant and interested in probiotics, discuss it with your healthcare provider, as individual circumstances vary. This research is interesting but not yet strong enough to change medical practice.

Pregnant women curious about optimizing their baby’s health should be aware of this research, but it’s too early to make decisions based on it. Healthcare providers interested in microbiome science and infant health will find this relevant. Parents of newborns won’t need to change anything based on these findings. People with specific health conditions should definitely consult their doctor before taking probiotics.

Any effects from prenatal probiotics appear within the first few days of a baby’s life but disappear by 2 weeks. By 6 months, there are no detectable differences between babies whose mothers took probiotics and those who didn’t. This suggests that if prenatal probiotics do help, the benefit would need to come from those early days, not from long-term changes.

Want to Apply This Research?

  • If a user is pregnant and considering probiotics, they could track: (1) which probiotic supplement they’re taking and dosage, (2) any digestive changes they notice, (3) adherence to the supplement schedule. After birth, they could note any differences in baby digestion or health, though this study suggests probiotic effects would be minimal.
  • A pregnant user could use the app to: set reminders to take a probiotic supplement at the same time daily if their doctor recommends it, log their adherence to the supplement routine, and track any side effects or digestive changes. After birth, they could monitor baby digestion patterns, though this study suggests prenatal probiotics won’t significantly change long-term outcomes.
  • For long-term tracking, users could monitor maternal digestive health during pregnancy and infant digestive health (stool frequency, consistency, comfort) in the first 6 months. However, this study suggests that prenatal probiotic effects are temporary, so dramatic long-term changes shouldn’t be expected. Focus tracking on the first 2 weeks postpartum when effects would be most visible.

This research is preliminary and should not be used to make medical decisions without consulting a healthcare provider. Prenatal probiotic supplementation is not yet standard medical practice. Pregnant women should always discuss any supplements with their obstetrician or midwife before use, as safety and appropriateness vary by individual health status. This study was small and showed only temporary effects, so results may not apply to all populations or all probiotic products. The study did not measure actual health outcomes in babies, only changes in bacteria composition. Parents should not make decisions about infant care based solely on this research.