In some maternity wards, babies delivered by caesarean (C)-section undergo a strange practice, called « Vaginal seeding »: one hour before the surgery, a sheet of gauze is inserted into the mother’s vagina, which is used, immediately after birth, to dab the baby in the mouth, on the face, and then on the rest of the body. This aims to mimic a “normal” delivery via the vaginal route, which is considered better physiologically, and is associated with better health outcomes further on (1).
“Recreating” a vaginal birth
But what is the point of recreating a vaginal birth? The rationale for vaginal seeding rests on the assumption that the greater susceptibility to diseases later in life, experienced by babies born by C-section (2), may be due, at least in part, to the gut microbiota, i.e to the community of microbes found in the intestines. Indeed, during pregnancy, the baby resides in a sterile womb and encounters microbes during labor (after the rupture of membranes) and at birth. This “bacterial baptism” is the first step in the colonisation of the newborn by microbes, on the skin and in the cavities, including the entire digestive tract from the mouth to the anus (3). The mode of birth conditions the first colonisers of the baby’s intestine, depending on which ones he or she meets first: the vaginal and perianal microbes of the mother in the case of a physiological birth, or the skin and environmental microbes in the case of a C-section (4).
Thus, children born via the birth canal have a gut microbiota mainly composed of bacteria called Lactobacillus, Prevotella, and Sneathia, whereas children born by C-section have a microbiota dominated by Staphylococcus, Corynebacterium, and Cutibacterium, and are colonised with a delay by genera such as Bacteroides and Bifidobacterium (2,5). It is assumed that the initial colonisation of the microbiota is crucial for the future health of the baby, since it conditions the maturation of the immune system, the neurodevelopment, as well as the metabolism. C-sections may disrupt mother-to-neonate transmission of specific microbial strains, linked to functional repertoires and immune-stimulatory potential during a critical window for neonatal immune system priming, which could explain why non-vaginally born babies are at higher risk later in life for health disorders such as asthma, atopic diseases, allergies, obesity, and even type 1 diabetes mellitus (6). In this perspective, vaginal seeding aims to reduce the gap in early microbial exposure of newborns between C-section and physiological delivery, and therefore to reduce the risk of developing health problems.
Some health benefits…
This remained to be demonstrated through clinical trials. The Inova’s randomised, double-blind study, which included 50 mother/child pairs who underwent C-section, suggested that this technique may be beneficial, as it increased the transmission of microbiota from mother to neonate (7). A non-randomised study that compared 79 babies born by C-section, including 30 swabbed with maternal secretions, to 98 vaginally-born ones, confirmed that vaginal seeding shifted the trajectory of the microbiota towards that of babies passed through the birth canal. (8). However, a small randomised study conducted on 25 C-section babies provided contradictory results, as no significant differences in fecal microbiota composition were found at one and three months between the babies who were given an oral preparation of vaginal microbes and those given a placebo (9). Moreover, regardless of the mode of delivery and exposure to vaginal microbes, the microbiota seems to converge around the age of one year (10). Finally, a randomised controlled study conducted on 120 C-section Chinese babies found no benefits of vaginal seeding on allergy risk during the first two years of life (11). Data are still lacking to confirm whether vaginal seeding could decrease the risk of other pathologies later on. Long-term studies still in progress will make it possible to settle this point.
But what if the altered “bacterial baptism” was not the major driver of microbiota dysbiosis, followed by health issues in C-section babies? Indeed, C-section is often preceded by a prophylactic antibiotic treatment (known to be deleterious to the microbiota), more often concerns low birth weight or premature babies, is less often followed by breastfeeding… When a C-section is planned, the baby does not undergo labor which is likely to modify the biochemical and hormonal signals that he or she receives. So many confounding factors that could impact the microbiota features as much, or even more than, the initial inoculation (12).
… but also potential risks
Besides, the safety of vaginal seeding is also questioned. Indeed, although no adverse effects have been reported from clinical trials, pregnant women who were enrolled were all screened negative for pathogens transmitted by vaginal fluids and/or other body fluids, such as group B streptococcus (the most common cause of sepsis in newborns), herpes simplex virus, Chlamydia trachomatis, or Neisseria gonorrhoeae (13). In common practice, women are not always tested for these pathogens during pregnancy, which would be necessary to ensure the safety of the practice and avoid transmission, bypassed in the case of C-section.
A practice that raises regulatory and ethical questions
Beyond the debate on the benefit/risk balance, this topic has raised regulatory and ethical questions. Vaginal secretions are considered as drugs in several countries, just like transplants prepared from stools or vaginal secretions in some restricted indications. This regulatory status is questionable. Indeed, the newborn is only exposed to the mother’s fluids, as if there were no C-section. By the way, vaginal seeding does not imply any processing or storage. Furthermore, from an ethical point of view, comprehensive and detailed information on the risks and benefits of this practice should be given to mothers before undergoing this procedure (1).
The debate is still ongoing as to whether vaginal seeding should become standard practice and should be offered to all mothers giving birth by C-section. Some scientists urge caution and support calls to stop this practice until robust evidence of need, efficacy, and safety is available (12). In a 2016 editorial of the British Medical Journal, key opinion leaders from the UK and Australia cautioned clinicians “not to perform vaginal seeding because [they] believe the small risk of harm cannot be justified without evidence of benefit.” Similarly, the American College of Obstetricians and Gynaecologists does not recommend the use of vaginal seeding outside of a research protocol approved by an independent ethics committee (1). On the other hand, vaginal seeding is considered effective and safe, and quite well accepted by pregnant women in New Zealand (14). As the benefits of breast milk are well-known, whether on gut microbiota establishment or future health outcomes, a public policy to encourage breastfeeding is likely a safe alternative to vaginal seeding.
1. Mueller NT, Hourigan SK, Hoffmann DE, Levy L, von Rosenvinge EC, Chou B, et al. Bacterial Baptism: Scientific, Medical, and Regulatory Issues Raised by Vaginal Seeding of C-Section-Born Babies. J Law Med Ethics J Am Soc Law Med Ethics. 2019 Dec;47(4):568–78.
2. Wampach L, Heintz-Buschart A, Fritz JV, Ramiro-Garcia J, Habier J, Herold M, et al. Birth mode is associated with earliest strain-conferred gut microbiome functions and immunostimulatory potential. Nat Commun. 2018 Nov 30;9(1):5091.
3. Milani C, Duranti S, Bottacini F, Casey E, Turroni F, Mahony J, et al. The First Microbial Colonizers of the Human Gut: Composition, Activities, and Health Implications of the Infant Gut Microbiota. Microbiol Mol Biol Rev. 2017 Nov 8;81(4):e00036-17.
4. Ronan V, Yeasin R, Claud EC. Childhood Development and the Microbiome-The Intestinal Microbiota in Maintenance of Health and Development of Disease During Childhood Development. Gastroenterology. 2021 Jan;160(2):495–506.
5. Dong TS, Gupta A. Influence of Early Life, Diet, and the Environment on the Microbiome. Clin Gastroenterol Hepatol Off Clin Pract J Am Gastroenterol Assoc. 2019 Jan;17(2):231–42.
6. Wampach L, Heintz-Buschart A, Fritz JV, Ramiro-Garcia J, Habier J, Herold M, et al. Birth mode is associated with earliest strain-conferred gut microbiome functions and immunostimulatory potential. Nat Commun. 2018 Nov 30;9(1):5091.
7. Mueller NT, Differding MK, Sun H, Wang J, Levy S, Deopujari V, et al. Maternal Bacterial Engraftment in Multiple Body Sites of Cesarean Section Born Neonates after Vaginal Seeding-a Randomized Controlled Trial. mBio. 2023 Apr 19;e0049123.
8. Song SJ, Wang J, Martino C, Jiang L, Thompson WK, Shenhav L, et al. Naturalization of the microbiota developmental trajectory of Cesarean-born neonates after vaginal seeding. Med N Y N. 2021 Aug 13;2(8):951-964.e5.
9. Wilson BC, Butler ÉM, Grigg CP, Derraik JGB, Chiavaroli V, Walker N, et al. Oral administration of maternal vaginal microbes at birth to restore gut microbiome development in infants born by caesarean section: A pilot randomised placebo-controlled trial. EBioMedicine. 2021 Jul;69:103443.
10. Kelly JC, Nolan LS, Good M. Vaginal seeding after cesarean birth: Can we build a better infant microbiome? Med N Y N. 2021 Aug 13;2(8):889–91.
11. Liu Y, Li HT, Zhou SJ, Zhou HH, Xiong Y, Yang J, et al. Effects of vaginal seeding on gut microbiota, body mass index, and allergy risks in infants born through cesarean delivery: a randomized clinical trial. Am J Obstet Gynecol MFM. 2023 Jan;5(1):100793.
12. Stinson LF, Payne MS, Keelan JA. A Critical Review of the Bacterial Baptism Hypothesis and the Impact of Cesarean Delivery on the Infant Microbiome. Front Med. 2018;5:135.
13. Jenmalm MC. Re: ‘Vaginal seeding’ after a caesarean section provides benefits to newborn children: AGAINST: Vaginal microbiome transfer – a medical procedure with clear risks and uncertain benefits. BJOG Int J Obstet Gynaecol. 2020 Jun;127(7):906.
14. Butler ÉM, Reynolds AJ, Derraik JGB, Wilson BC, Cutfield WS, Grigg CP. The views of pregnant women in New Zealand on vaginal seeding: a mixed-methods study. BMC Pregnancy Childbirth. 2021 Jan 12;21(1):49.