Oops, C-section does NOT impact the neonatal gut microbiome much at all!

Gut bacteria , gut flora, microbiome. Bacteria inside the small intestine, concept, representation. 3D illustration.

The more research we do, the LESS support there is for the claim that C-sections impact the neonatal microbiome in ways that are ultimately harmful to health.

Research on the impact of C-section on the neonatal microbiome has been plagued with major problems, the most important of which is the naturalistic fallacy: the belief that if something is a certain way in nature, that must be the best possible way. Since passage through the vagina was the only way to give birth for most of human history, there are many people who believe it must be the best way to give birth.

The claim that C-sections alter the neonatal microbiome in ways that are harmful has never been proven and is likely to be nothing more than wishful thinking.

Vaginal birth is obviously not the best way to maximize maternal and infant survival. C-sections save literally hundreds of thousands of mothers and babies each and every year. Research has shown that a minimal C-section rate of 19% is necessary to achieve low maternal and perinatal mortality. Those clinging to the naturalistic fallacy continue to search for something, anything, with which to demonize C-sections. The latest object of their affections is the neonatal microbiome. Many within the natural childbirth industry, and some within the medical profession, are claiming that C-section alters the neonatal microbiome in ways that are ultimately harmful to longterm health.

Last year I reported on the largest study to that date that looked at the impact of mode of delivery on the neonatal microbiome. Maturation of the infant microbiome community structure and function across multiple body sites and in relation to mode of delivery was published in Nature Medicine.

The authors found:

…[T]here was no discernable effect of the cesarean mode of delivery on the early microbiota beyond the immediate neonatal period (and never inclusive of that in the meconium or stool) …

Now comes a new literature review that further undermines the claim that C-sections alter the neonatal microbiome. A Critical Review of the Bacterial Baptism Hypothesis and the Impact of Cesarean Delivery on the Infant Microbiome was published just this week.

The authors take aim at the bacterial baptism hypothesis.

…[E]pidemiological studies have linked Cesarean delivery with increased rates of asthma, allergies, autoimmune disorders, and obesity. Mode of delivery has also been associated with differences in the infant microbiome. It has been suggested that these differences are attributable to the “bacterial baptism” of vaginal birth, which is bypassed in cesarean deliveries, and that the abnormal establishment of the early-life microbiome is the mediator of later-life adverse outcomes observed in cesarean delivered infants. This has led to the increasingly popular practice of “vaginal seeding”: the iatrogenic transfer of vaginal microbiota to the neonate to promote establishment of a “normal” infant microbiome.

The investigators who first proposed the bacterial baptism hypothesis noted differences in the microbiota of the nose and mouth between infants delivered by C-section vs vaginal birth.

Given that neonates were swabbed within seconds of delivery, and thus it would be coated with vaginal fluids, this result is hardly surprising. This does not necessarily demonstrate colonization, however.

What about the initial neonatal gut microbiome?

Numerous studies describing the bacterial microbiota of first pass meconium (the first fecal material, passed shortly after birth) support the notion that CSD and VD neonates do not differ in their bacterial microbiomes in the first few days following birth.

How about thereafter?

Although most studies report no differences in the microbiome of VD and CSD neonates in the first days of life, evidence is compelling that differences begin to develop shortly thereafter and persist for weeks or months.

And the differences almost entirely disappear when infants start eating solid food.

Do the temporary differences reflect mode of delivery or confounding factors? It is very likely they are the result of confounding factors such as:

1. Antibiotics:

All mothers delivering by CS are administered intrapartum antibiotic prophylaxis (IAP), as is routine for any type of surgery. In some countries, IAP is administered after the cord is clamped, minimizing direct antibiotic exposure of the neonate. In others, antibiotics are given prior to commencement of surgery… Mothers delivering vaginally are not routinely administered antibiotics, with the notable exception of those who are vaginally colonized with Group B Streptococcus (GBS). Overall, rates of intrapartum antibiotic use are low in vaginally delivering mothers.

2. Labor:

…[L]abor causes changes in levels of endocrine, inflammatory, and contractile factors. These changes might influence the maternal microbiome or the establishment of the neonatal microbiome. Additionally, labor is often accompanied by rupture of the fetal membranes, exposing the fetus to maternal vaginal bacteria…

3. Breastfeeding:

Source tracking studies have shown that 27% of an infant’s gut microbiota is vertically derived from its mother’s breast milk, while an additional 10% is sourced from the skin around the areola.

4. Maternal obesity:

Obesity and high-fat diets have repeatedly been correlated with aberrations to the gut microbiome in humans. Maternal obesity alters the maternal gut microbiome during pregnancy, and the milk microbiome during lactation …

The microbiome of obese mothers may have a harmful effect on weight gain in toddlers:

Mother-to-child transmission of obesogenic microbes continues to disrupt microbiome patterns into early childhood. Galley et al. found that the gut microbiomes of toddlers born to obese mothers of high socioeconomic status (SES) clustered away from those of toddlers born from lean high SES mothers. In particular, children born to obese mothers had differences in abundances of Faecalibacterium spp., Eubacterium spp., Oscillibacter spp., and Blautia spp., all of which have been correlated to diet and body weight in previous studies.

5. Gestational age and NICU exposure:

Rates of CS delivery increase with decreasing gestational age at delivery. Preterm infants differ from their full-term counterparts in terms of their gut microbiota, immune development, and health outcome…

The NICU environment is likely to influence the microbiome, so duration of residence and the environmental microbiome of the unit are likely to have a significant impact…

6. Inter-individual variation:

Studies that compare the microbiomes of infants born by CS or vaginal delivery must have sufficient power to account for variation in the maternal microbiome, as this is likely to exert a large influence on an infant’s microbiome through breastfeeding and physical contact. Large cohorts are thus required with the ability to control variables, such as home environment, presence of pets, and exposures to other microbiome-altering factors including hygiene and maternal/infant diet.

To date there have been no studies involving large cohorts.

In summary:

…[G]iven the numerous and significant confounding factors present in studies comparing the microbiota after CS and vaginal delivery, it is impossible to say with any certainty that it is the act of delivering vaginally itself which confers this optimal microbiota, or what species/genera of bacteria might be responsible. Differences in antibiotic administration, labor onset, maternal body weight and diet, gestational age, and breastfeeding frequency and duration undoubtedly contribute to differences observed between CSD and VD infants. Further, it is likely that differences between CSD and VD infants do not develop until several days after birth. Given recent evidence that infant microbiome colonization begins in utero, it may be that the importance of “bacterial baptism” of vaginal birth has been significantly over-estimated.

Although numerous studies have demonstrated an association between CS delivery and altered microbiome establishment, no studies have confirmed causality.

The authors recommend abandoning the practice of vaginal seeding:

Health practitioners should not bow to popular pressure to perform vaginal seeding in the absence of data on need, effectiveness, and appropriate protocols for ensuring safety.

The natural childbirth industry is not going to give up on demonizing C-sections any time soon, but women need to know that the claim that C-sections alter the neonatal microbiome in ways that are harmful has never been proven and is likely to be nothing more than wishful thinking.

  • Mike Stevens

    I can never understand these folk using “vaginal seeding” to give their sectioned infants a dose of natural bacteria to boost their microbiome.

    What they need to do is “anal seeding”, and smear some of their own faeces into junior’s mouth.
    But that doesn’t sound so “natural-touchy-feely-goody goody”, does it?

  • Peter Harris

    “Source tracking studies have shown that 27% of an infant’s gut microbiota is vertically derived from its mother’s breast milk…”

    Evidence that this website is hypocritical, ill informed, inconsistant and just Gila.

    You don’t advocate breastfeeding, so that quote is irrelevant, along with the 27% of the gut microbiome

  • Megan

    Glad to see this since I will be having my repeat CS on Thursday and had no intention of wiping kiddo’s face with my vaginal secretions. Gross. Of course, baby’s gut microbiole will be screwed anyway since we are EFF. /s

    Incidentally, doc feels this baby is likely to be 9 lbs or more. Thank goodness that I don’t have to push him/her out!!

  • Cat

    I’m very far from being in love with the idea of vaginal birth this week. Over the past few days I’ve read a family member’s account of the death of her baby after a botched delivery, which she wrote at her counsellor’s request*, and I’ve heard the grim story of another family member’s recent childbirth experience (short version: it appears that they tore a load of her scar tissue from recent abdominal surgery in their attempts at inducing her, before deciding that a pile-up of risk factors including fetal macrosomia and pre-eclampsia meant that vaginal delivery was a bad call after all. I can’t comment on the science but, compared to my elective c-section, it seems so barbaric I could cry for her).

    * The counselling is very belated but I’m so proud of her.

  • Abi

    This seems like an obvious question, but has anyone specifically compared the neonatal microbiome outcomes of mothers who delivered vaginally but had antibiotics during labour with those who had a CS and antibiotics prior to delivery/cord clamping and compared with those who did NOT have this medication in both scenarios – in order to control for antibiotics?

    These drugs are one of a few things we already know to have some impact on gut flora, so I’ve always suspected this might be the confounding factor in any differences observed, just as Dr Tuteur suggests here. It seems fairly likely that it’s the drugs, and nothing to do with the mode of birth that’s making any different at all. But surely this could be fairly easily tested?

    • Amy Tuteur, MD

      To my knowledge, no one has yet looked at that.

    • Sue

      That would seem to make sense.

      They should stratify for a whole bunch of confounders: Timing of rupture of membranes, length of delivery, CS pre- or during labor etc

    • mabelcruet

      Somewhat related-in the UK, we don’t routinely screen for GBS in pregnancy. Women known to carry GBS are offered antibiotics in labour, but the Royal College of Obstetrics and the UK screening programme doesn’t recommend routine screening for GBS in asymptomatic women: some of the arguments are that you would end up treating a lot of women with antibiotics who didn’t actually need them (for those women with GBS that doesn’t turn pathological, which runs a risk of increasing bacterial resistance), and we don’t know what the impact would be on babies in utero (and given that if you give a pregnant woman GBS eradication, a significant proportion will re-acquire GBS and so might end up with repeated courses of antibiotics which will obviously have an increased risk of impact on the baby).

      • AnnaPDE

        But isn’t the possible reinfection with GBS why women in countries where GBS screening is standard get antibiotics during labour, not beforehand? My stepson’s mother screened positive for GBS during her second pregnancy and there wasn’t any talk of eradication during the pregnancy.

        • mabelcruet

          I think so, it allows for a bit of forward planning for labour. In UK they don’t screen because they wouldn’t do anything about it if they found it, and mothers only get antibiotics during labour if GBS was picked up fortuitously (like if mum has UTI, or had GBS in a previous pregnancy). It means that every so often we get a case of a stillbirth or neonatal death as a result of GBS where mum wasn’t known to be a carrier, and that flares up into a media outcry about GBS screening and how UK mums and babies are being put at risk. But the Royal College Obs and Gynae say the evidence shows screening has no benefit and eradication prior to birth doesn’t affect neonatal infection rates and doesn’t impact on mortality. If mum is symptomatic, then that’s different, but for low risk asymptomatic mums, screening isn’t recommended.

          • fiftyfifty1

            Yes, eradication during pregnancy doesn’t work because the colon is colonized with the GBS and it’s so difficult to sterilize a colon. But as for the idea that screening has “no benefit” that’s not the case. Screening and treating women with IV abx in labor does prevent GBS infection in the infants. But the number needed to treat is huge. Too huge for the Royal College to get on board.

        • niteseer

          My first child died of Group B strep meningitis when she was 8 days old. They didn’t test back then, in 1978. Two weeks ago, my daughter in law gave birth to my grand son, and received IV antibiotics due to a positive strep screen. I hold him now, and thank God that times have changed.
          I am surprised that the UK doesn’t screen for this, and treat it. Anyone who has lost a child to this terrible, and preventable, infection, would be glad to tell them expense is negligible compared to the benefit.

      • swbarnes2

        Is eradication the goal of giving antibiotics during labor? I figured it was just suppression.

        • mabelcruet

          Antibiotics during labour are to prevent GBS in the baby, not eradicate from maternal vagina. They are only given once mum is in labour. But if she has preterm membrane rupture (before 37 weeks), antibiotics are given then even if she isn’t in labour to reduce the risk of fetal transmission.

          It’s an issue that blows up every now and again (usually in newspaper like the Daily Mail) where the story is along the lines of ‘ if the medics knew I had GBS, why didn’t I get antibiotics to clear it early in pregnancy?’. The media reports don’t differentiate between normal commensal carriage and pathological infection.

      • Given that the US does screen, we should know these things, shouldn’t we?

        • mabelcruet

          I think that US screens women at 35-37 weeks, but doesn’t go for eradication antibiotics for positive results, just as forewarning for antibiotics when in labour (but being neither an obstetrician or an American, you’d best wait for a more informed answer!)

  • PeggySue

    Well, I am stunned. Simply stunned, I tell you. (That was sarcasm.)

  • Namaste

    This is completely totally 100% OT, but….l really like you guys…..and tomorrow I am graduating with my Masters in Social Work.

    • Empress of the Iguana People

      congrats!

    • kilda

      congratulations!!!

    • PeggySue

      Congratulations!!!!!

    • Cat

      Congratulations – that’s terrific!

    • Who?

      Well done great achievement!

    • Sue

      Great – congrats!

    • Daleth

      Congrats!

  • MaineJen

    So, can we stop the disgusting practice of vaginal seeding now? Pretty please?

    • Empress of the Iguana People

      The hypothesis wasn’t completely out there, but ick. I’d have needed a much stronger set of studies than the ones that were out to have tried it on my kids.

    • Zornorph

      I can’t imagine the response if fathers started demanding to wipe their ball sweat on their newborn babies faces to ‘promote bonding’ or some such bit of lunacy.

      • Bugsy

        I’ve got to stop reading this page while eating dinner!! 😛