Introduction
Human gut microbiomes are the collection of bacteria, viruses, fungi, protozoa, and eukaryotes colonizing the human gastrointestinal tract. These microbiomes have high functional capacity and benefit the host in several ways. The diversity of gut microbiomes is shaped by the host and many environmental factors (1, 2). Genetics, mode of delivery, diet, population, and location can diversify these gut microbes (1-4). Loss of gut microbiome diversity and balance can cause diabetes, allergy, autoimmune diseases, and obesity(2, 5).
The changes in gut microbiome diversity during pregnancy increase some risks of pregnancy complications, such as gestational diabetes, preeclampsia, maternal infection, growth restriction, and intrauterine demise (4, 6). Common bacteria in neonatal gut microbiomes are Actinobacteria (Bifidobacterium) (7), Firmicutes (7, 8), and Lactobacillus(9). Studies show a relationship between maternal and neonatal gut microbiome diversity (4, 6). The gut microbes can pass from mothers to babies via many routes, such as via the vagina, the gastrointestinal tract, the skin, breast milk, and subsequently colonize the infant’s gut immediately after birth(4, 8). The infant’s immune system is an important system that can be affected by this gut microbiota diversity and potentially affect long-term outcomes (10). Because the vagina is one of the routes by which mothers pass microbiotas on to their babies, the question of whether the route of delivery can affect the infant’s microbiome can be posed.
The cesarean section rate has been increasing over the last few decades. Data from the World Health Organization (WHO) in 2021 showed the cesarean rate was 21%, compared with 7% in 1990(11). Infants born via cesarean section have different exposures to substances from those born vaginally (5). There has been conflict regarding whether the mode of delivery can alter a newborn’s gut microbiome diversity.
There are many methods widely used to identify gut microbiomes, one of which is metagenomic sequencing. Using a 16S rRNA gene sequencing technique, uncultured microbiomes can be identified. It can provide information on the complete genome in less time and is more accurate than the classic method. This method is widely used today(12, 13).
Attempts to study neonatal outcomes of cesarean delivery related to gut microbiomes in early life have been made and are increasing in many countries. Yet, there have still been no studies carried out in Thailand. Understanding the differences in neonatal gut microbiomes between those delivered via vaginal delivery and those delivered by cesarean section in the Thai population, including the factors that can affect the diversity of gut microbiomes, may help researchers identify risk factors, preventive methods, or interventions to help promote the long-term outcomes of those delivered via cesarean section.