According to Gram Research analysis, pregnant women with gestational diabetes have different vaginal bacteria than healthy pregnant women, with less protective Lactobacillus (79.8% vs 87.4%) and nearly seven times more Gardnerella bacteria (9.7% vs 1.4%). Women with gestational diabetes who had higher Gardnerella levels were more likely to have smaller babies at birth, suggesting that vaginal bacteria balance may influence fetal growth in this population. However, this is early-stage research, and more studies are needed before doctors might use this information clinically.
Researchers discovered that pregnant women with gestational diabetes have different bacteria in their vaginas compared to healthy pregnant women. Specifically, they found less of a protective bacteria called Lactobacillus and more of a bacteria called Gardnerella. Interestingly, women whose babies were smaller at birth had even higher levels of Gardnerella. This suggests that the balance of bacteria during pregnancy might play a role in how much babies grow. The study included 60 women with gestational diabetes and 119 healthy pregnant women, all tested in their third trimester. While these findings are preliminary, they open new questions about how pregnancy health and bacteria are connected.
Key Statistics
A 2026 case-control study of 179 pregnant women published in Diabetologia found that women with gestational diabetes had significantly lower Lactobacillus abundance (79.8% vs 87.4%) and nearly seven times higher Gardnerella abundance (9.7% vs 1.4%) compared to healthy pregnant women.
Among 60 women with gestational diabetes, those with higher Gardnerella bacteria levels had higher fasting blood glucose levels and were more likely to have babies in the lower birthweight percentile, with 44.4% of women carrying smaller babies having non-Lactobacillus-dominated vaginal communities versus 12.1% of women with average-sized babies.
A 2026 observational study found that Gardnerella abundance in the vaginal microbiome correlated positively with fasting glucose levels (r=0.3617, p=0.007) and inversely with fetal birthweight percentile (r=-0.2774, p=0.032) in women with gestational diabetes.
Only 73.3% of pregnant women with gestational diabetes had Lactobacillus-dominated vaginal communities compared to 86.6% of healthy pregnant women in a 2026 study, representing a significant shift in protective bacteria during pregnancy with diabetes.
The Quick Take
- What they studied: Whether the types of bacteria living in the vagina during late pregnancy differ between women with gestational diabetes and healthy pregnant women, and whether these bacteria affect baby size at birth.
- Who participated: 179 pregnant women in their third trimester: 60 with newly diagnosed gestational diabetes managed through diet alone, and 119 healthy pregnant women without diabetes. All were recruited at a single hospital center.
- Key finding: Women with gestational diabetes had less of the ‘good’ bacteria Lactobacillus (79.8% vs 87.4%) and more Gardnerella bacteria (9.7% vs 1.4%). Among women with gestational diabetes, higher Gardnerella levels were linked to smaller babies at birth.
- What it means for you: This research suggests that vaginal bacteria balance during pregnancy may influence both blood sugar control and baby growth in women with gestational diabetes. However, this is early-stage research, and more studies are needed before doctors might use this information to change pregnancy care. Talk to your healthcare provider about your individual pregnancy health.
The Research Details
This was a case-control study, which means researchers compared two groups of pregnant women: those with gestational diabetes and those without. All participants had vaginal swabs collected during their third trimester (the final three months of pregnancy). The researchers then analyzed the DNA from bacteria in these swabs to identify which types of bacteria were present and in what amounts.
The study used a technique called 16S rRNA gene sequencing, which is like taking a detailed census of all the bacteria living in the vagina. This method can identify hundreds of different bacterial species from a single sample. The researchers then looked for patterns—did women with diabetes have different bacterial communities than healthy women? Did the bacteria patterns relate to blood sugar levels or baby size?
This approach is observational, meaning the researchers watched and measured what naturally occurred rather than randomly assigning women to different treatments. This type of study is good for finding associations (things that happen together) but cannot prove that one thing causes another.
Understanding the vaginal microbiome during pregnancy is important because the vagina is not sterile—it naturally contains many bacteria. These bacteria can affect pregnancy health in ways scientists are still discovering. By comparing women with and without gestational diabetes, researchers can identify whether diabetes changes the bacterial community. If certain bacteria are linked to worse outcomes (like smaller babies), this could eventually lead to new ways to support pregnant women’s health.
This study has several strengths: it used modern DNA sequencing technology, included a reasonable sample size (179 women), and was published in a respected journal (Diabetologia). However, readers should know that some findings were based on small numbers and used statistical tests that were not adjusted for multiple comparisons, which can sometimes lead to false positives. The associations between bacteria and baby size were modest, meaning other factors also play important roles. The study was observational, so it cannot prove that bacteria changes cause smaller babies—only that they occur together.
What the Results Show
The researchers found clear differences in vaginal bacteria between the two groups. Women with gestational diabetes were less likely to have vaginal communities dominated by Lactobacillus (the ‘good’ bacteria)—only 73.3% compared to 86.6% of healthy women. When Lactobacillus was present, it made up a smaller percentage of the total bacteria in women with diabetes (79.8% vs 87.4%).
At the same time, Gardnerella bacteria were much more common in women with gestational diabetes. This bacteria made up 9.7% of the vaginal community in women with diabetes but only 1.4% in healthy women—nearly seven times higher. These differences were statistically significant, meaning they were unlikely to be due to chance.
Within the group of women with gestational diabetes, those with higher Gardnerella levels had higher fasting blood sugar levels. Additionally, women whose babies were smaller at birth (below the 50th percentile for their gestational age) had significantly more Gardnerella bacteria than women whose babies were average-sized or larger. Specifically, 44.4% of women with smaller babies had non-Lactobacillus-dominated communities compared to only 12.1% of women with average or larger babies.
The overall diversity of bacteria (how many different types were present) was similar between the two groups, suggesting that women with gestational diabetes didn’t have fewer types of bacteria—just a different balance. The bacterial composition differences were statistically significant when researchers looked at the overall community structure, indicating that the pattern of change was consistent across the study population. When researchers excluded samples with extremely high Gardnerella levels, the associations became weaker, suggesting that a subset of women with very high Gardnerella levels drove some of the findings.
Previous research has shown that pregnancy changes the vaginal microbiome, and that certain conditions like bacterial vaginosis (an imbalance of vaginal bacteria) can affect pregnancy outcomes. This study adds new information by specifically examining gestational diabetes and identifying Gardnerella as a potentially important bacterium in this context. The finding that Lactobacillus is protective aligns with decades of research showing that Lactobacillus-dominated communities are generally associated with vaginal health. However, the specific link between Gardnerella and fetal growth in gestational diabetes is relatively novel and requires confirmation in larger studies.
Several limitations should be considered. First, this was a single-center study, so results may not apply to all populations. Second, the study was observational, so it cannot prove that Gardnerella causes smaller babies—only that they occur together. Third, the associations were modest in strength, meaning bacteria are likely just one of many factors affecting baby size. Fourth, some statistical tests were not adjusted for multiple comparisons, which increases the chance of false positives. Finally, the study did not measure whether women had symptoms of bacterial vaginosis or other infections, which could have influenced results. The researchers also noted that associations weakened when excluding extreme cases, suggesting some findings may be driven by a small number of women with very high Gardnerella levels.
The Bottom Line
Based on this early-stage research, there are no specific clinical recommendations yet. Women with gestational diabetes should follow their healthcare provider’s standard care, which typically includes dietary management, blood sugar monitoring, and regular prenatal visits. This research is exploratory and suggests future directions for study rather than immediate changes to clinical practice. Healthcare providers may eventually use vaginal microbiome information to better understand pregnancy complications, but this is not yet standard care.
This research is most relevant to pregnant women with gestational diabetes, their healthcare providers, and researchers studying pregnancy complications. Women planning pregnancy or currently pregnant should discuss their individual risk factors with their doctors. This research is not yet actionable for the general public but may inform future clinical guidelines. Women with gestational diabetes should not attempt to change their vaginal bacteria based on this single study.
This is preliminary research, and it typically takes 5-10 years for findings from observational studies to translate into clinical recommendations. Larger studies would need to confirm these associations, and researchers would need to determine whether changing vaginal bacteria could actually improve outcomes. In the meantime, standard gestational diabetes care remains the evidence-based approach.
Frequently Asked Questions
What is gestational diabetes and how does it affect pregnancy?
Gestational diabetes is high blood sugar that develops during pregnancy in women who didn’t have diabetes before. It affects 2-10% of pregnancies and can increase risks for both mother and baby, including larger babies, birth complications, and later-life diabetes. Managing blood sugar through diet and monitoring is the standard treatment.
What is the vaginal microbiome and why does it matter during pregnancy?
The vaginal microbiome is the community of bacteria living in the vagina. During pregnancy, these bacteria can affect maternal health and fetal development. A healthy vaginal microbiome is typically dominated by Lactobacillus bacteria, which protect against infections and maintain proper pH balance.
Can I change my vaginal bacteria if I have gestational diabetes?
This research is too preliminary to recommend specific interventions. Standard gestational diabetes management—controlling blood sugar through diet, exercise, and monitoring—remains the evidence-based approach. Talk to your healthcare provider before trying probiotics or other microbiome-targeting treatments, as their effectiveness during pregnancy is unproven.
Does this research mean my baby will be smaller if I have gestational diabetes?
No. This study found an association between certain bacteria and smaller babies, but bacteria are just one of many factors affecting fetal growth. Most babies born to women with well-managed gestational diabetes are healthy and normal-sized. Work with your healthcare team to manage your blood sugar, which is the proven way to support healthy fetal growth.
Should I get my vaginal bacteria tested if I have gestational diabetes?
Vaginal microbiome testing is not yet part of standard pregnancy care, even for women with gestational diabetes. This research is exploratory and may eventually inform clinical practice, but currently, standard prenatal care and blood sugar monitoring are the recommended approach. Discuss any concerns with your healthcare provider.
Want to Apply This Research?
- For women with gestational diabetes using a pregnancy health app, track fasting blood glucose levels daily and note any vaginal symptoms (discharge changes, odor, itching). This creates a personal record to discuss with your healthcare provider and may help identify patterns between blood sugar control and vaginal health.
- While this research is still preliminary, women with gestational diabetes can use an app to monitor their diet quality and blood sugar control, which are proven to help manage gestational diabetes. Maintaining good blood sugar control through diet and exercise remains the primary evidence-based approach. If your app includes a symptom tracker, note any vaginal symptoms to discuss with your doctor.
- Use your app to track: (1) daily fasting blood glucose readings, (2) dietary intake and carbohydrate choices, (3) physical activity, and (4) any vaginal symptoms. Share this data with your healthcare provider at prenatal visits. This comprehensive tracking helps your doctor assess your overall pregnancy health and may eventually help identify which women need additional monitoring.
This article summarizes research findings and is not medical advice. Gestational diabetes requires individualized medical care from qualified healthcare providers. If you are pregnant or planning pregnancy, discuss your risk factors, screening, and treatment options with your obstetrician or midwife. Do not attempt to diagnose or treat gestational diabetes or vaginal conditions based on this article. The findings presented are preliminary and should not change your current pregnancy care without guidance from your healthcare team. Always consult with your doctor before starting new supplements, probiotics, or treatments during pregnancy.
This research translation is published by Gram Research, the science division of Gram, an AI-powered nutrition tracking app.