The Dilemma: Necessary Treatment Versus Microbiome Impact

Antibiotics during pregnancy are sometimes medically necessary and potentially life-saving. Group B Streptococcus (GBS) prophylaxis, urinary tract infections, and bacterial vaginosis all require antibiotic treatment to protect both mother and baby. The challenge is that these same antibiotics significantly alter the maternal microbiome, which is the primary source of bacteria that will colonise the newborn's gut.

Approximately 40% of pregnant women receive antibiotics at some point during pregnancy or labour. Understanding the impact on the infant microbiome and knowing how to mitigate it is essential knowledge for expecting parents.

How Maternal Antibiotics Affect the Infant Microbiome

The Vertical Transmission Pathway

During vaginal delivery, the infant is exposed to maternal vaginal and faecal bacteria, which initiate gut colonisation. During breastfeeding, bacteria from the maternal gut travel to breast milk through an entero-mammary pathway, providing ongoing microbial seeding. When the mother's microbiome is disrupted by antibiotics, the bacteria she transfers to her infant are altered accordingly.

A 2016 study in mBio found that infants born to mothers who received intrapartum antibiotics (during labour) had significantly reduced Bifidobacterium colonisation and increased Enterobacteriaceae (a family containing many pathogenic species) compared to infants of untreated mothers. These differences persisted for up to 12 weeks after birth.

Important context: Not all antibiotics are equally disruptive. Narrow-spectrum antibiotics have less impact on the microbiome than broad-spectrum ones. If antibiotics are necessary, discuss with your healthcare provider whether a narrower-spectrum option is appropriate for your situation.

Timing Matters

The timing of antibiotic exposure influences the degree of microbiome disruption:

  • First trimester: impacts the maternal microbiome during the period when maternal gut bacteria are being selected for eventual transfer
  • Third trimester: disrupts the microbiome closest to delivery, directly affecting the composition of bacteria available for vertical transmission
  • Intrapartum (during labour): the most studied timing, with clear evidence of reduced beneficial bacteria in the newborn gut

Documented Consequences for the Infant

Research has linked prenatal and intrapartum antibiotic exposure to several outcomes in the infant:

  • Increased risk of allergic diseases: a meta-analysis of 22 studies found that prenatal antibiotic exposure increased childhood asthma risk by 20%
  • Higher rates of eczema: particularly when antibiotics were used in the second or third trimester
  • Altered immune development: reduced Treg cell populations and skewed Th1/Th2 balance in infants exposed to maternal antibiotics
  • Increased obesity risk: several studies have found associations between prenatal antibiotic exposure and childhood overweight, possibly mediated through metabolic programming via the microbiome

When Antibiotics Are Necessary

This information should not discourage anyone from taking medically necessary antibiotics during pregnancy. Untreated GBS can cause life-threatening neonatal sepsis. Untreated UTIs can progress to pyelonephritis and preterm labour. Bacterial vaginosis increases the risk of preterm birth. The risks of not treating these conditions far outweigh the microbiome impact, which can be mitigated.

Strategies to Support Microbiome Recovery

During and After Antibiotic Treatment

  • Take a probiotic during and after the antibiotic course: Saccharomyces boulardii is unaffected by antibiotics and can be taken simultaneously. Lactobacillus rhamnosus GG should be taken two hours apart from the antibiotic dose
  • Increase fermented food consumption: kefir, sauerkraut, and natural yoghurt provide live bacteria to help recolonise the gut
  • Eat abundant prebiotic fibre: garlic, onions, bananas, asparagus, and oats feed surviving beneficial bacteria and support their recovery

After Birth

  • Breastfeed if possible: breast milk contains HMOs that specifically support Bifidobacterium colonisation, helping to compensate for antibiotic-related depletion
  • Maximise skin-to-skin contact: transfers maternal skin bacteria to the newborn
  • Discuss infant probiotics with your paediatrician: B. infantis EVC001 or L. reuteri DSM 17938 may help restore beneficial colonisation
  • Avoid unnecessary infant antibiotic use: further courses compound the disruption

How GutIQ Helps You Prepare

Entering pregnancy with a healthy microbiome gives your baby the best possible start. GutIQ evaluates your current gut health and identifies specific areas for improvement, so you can optimise your microbiome before conception or during pregnancy. Understanding your gut status also helps you make more informed decisions when discussing antibiotic use with your healthcare team, armed with knowledge about your baseline and what recovery strategies will be most effective.