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.