Interpretation
In 1985, Lince20 first reported that the FEB is an
abnormal ultrasound sign. Slotnick5 classified the
strong echo of the intestine into three grades. In this study, all the
cases were intestinal hyperechoic grade > 2.
In recent years, the intestinal flora play an important role in a number
of diseases, such as premature delivery,
obesity.21Therefore,we hypothesized that
hyperechogenic bowel might be related to intestinal flora.
The study showed that there were abundant bacteria in the meconium of
newborns, which is consistent with the results of Jimenez et
al.11A reduction of the α diversity of the intestinal
flora is causal of many diseases, including autoimmune diseases,
obesity.22-23 In this study there were no significant
differences in the α diversity of meconium flora among the three groups
and the composition of intestinal flora in the three groups was similar,
which may be one of the reasons for the good outcome of most newborns
with FEB. Pately et al.24 reported that if the fetus
with echogenic bowel can be delivered normally, there are no severe
pathologic changes in the intestinal tract after delivery, which may be
explained by our experimental results. In this study the structure of
intestinal microbiota of the three groups of newborns was similar, withProteobacteria and Firmicutes the two major components of
the phylum, which is in agreement with Collado et
al.10
What are the acoustic physical reasons for an echogenic bowel? Some
researchers believe that the components in the lumen of the intestine
are responsible for the formation of echogenic bowel, such as meconium.
During the second trimester of pregnancy, echogenic bowel may be caused
by the concentration and viscosity of the intestinal secretions. With
the gradual release of these concentrated substances into the intestine,
the grade of FEB will also decrease.5
IUGR is the main cause of perinatal death and morbidity. IUGR leads to
the delayed development of colonic mucosa and the destruction of
intestinal mucosal barrier, including intestinal epithelium, mucous
layer, and other components.25 Mesenteric ischemia and
impaired intestinal motility are the result of fetal blood
redistribution in newborns with IUGR, thus there is a preferential
supply of blood flow to the heart and brain and reduced blood flow to
other organs of the fetus, including the intestine, while FEB is one of
the features representing IUGR.26 Sepulveda et
al.27 considered that FEB in newborns with IUGR
indicates that intestinal peristalsis slows down and meconium is thick
due to intestinal ischemia.
CF is an autosomal recessive genetic disease. Because of the incomplete
function of the CFTR gene, the airway mucus secretion increases and the
mucous membranes thicken, leading to chronic lung
infections.28 The prenatal diagnosis of fetuses with
FEB requires further consultation with parents whether or not the
fetuses have CF because FEB is closely related to the CF pathologic
state.29 Thus, the appearance of FEB may also be due
to the viscous secretion of mucus. Ultrasound reveals scattering and
shows strong echoes of the fetal intestine.
Therefore, we found that the formation of FEB may be related to the
secretion of mucus in the intestinal tract. The difference in bacterial
abundance in the intestinal tract may promote or inhibit the secretion
of mucus. Thus, different concentrations of mucus contributed to
intestinal echoes. In the fetal small intestine, mucus is secreted as
early as the 10th week gestation. Mucus secretion is helpful for the
formation of meconium.30 The surface of the fetal
intestinal epithelium is covered with a thick layer of mucus, forming a
hydrophilic network structure.30-32 The mucus layer is
secreted by goblet cells of the intestinal
epithelium.33 Mucus also includes water, ions, and
immune mediators, which help to eliminate intestinal
pathogens34-35 and maintain the homeostasis of host
microorganisms.36 There were significant differences
in the abundance of E. coli / Shigella ,Staphylococcus , Methylrod, and Curvibacter among
the three groups of newborns, which may have resulted in different
concentrations of mucus in the intestine and different intestinal
echogenicity. With time, the abundance of bacteria in the intestinal
tract changes, the mucus is diluted, and the echo is reduced. Therefore,
part of FEB gradually disappears as gestational age increases.
Therefore, we speculate that the difference in the abundance of
intestinal flora might be related to echogenic bowel.
Caspi et al.8 believe that the bacteria propagate,
ferment, and metabolize in the intestine to produce intestinal gas,
which is characterized by echogenic bowel after the fetus swallows
amniotic fluid. Therefore, we propose that the formation of FEB may be
related to the accumulation of intestinal gas, which may be related to
intestinal bacteria. In the current study, a different abundance ofGammaproteobacteria , Fusobacteria ,Enterobacteriaceae , and E. coli were detected in the EB
and C-EB groups.
Do these bacteria produce gas that makes hyperechogenic bowel? SomeEnterobacteriaceae strains can produce
amines.37 Barton et al.38-39 found
that many bacteria can decompose cysteine into H2S gas
in the colon, including Clostridium , Enterobacter ,E. coli , and Vibrio desulfuricus . This suggest that the
reason for the hypergenic bowel may be related to the gas produced by
the microbiota. The accumulation of intestinal gas and multiple
interfaces lead to FEB. Ljssennagger et al.40 proposed
that H2S gas interacts with the intestinal mucous layer
to regulate intestinal inflammation. We speculate that the intestinal
microbiota might affect the secretion of intestinal mucus and intestinal
gas to make a strong intestinal echo.
In this study the abundance of Firmicutes in the EB group was
higher than the C-EB and control groups, while the abandance of
Fusobacteria in the C-EB and EB groups was significantly lower than the
control group. Indiani et al.41 showed that the
abundance of Firmicutes was positively correlated with the
increase in the weight of children. The higher the abundance ofFirmicutes , the higher the risk of obesity in children. This
finding suggests the EB group has a higher risk of obesity in childhood.Fusobacteria is related to premature delivery, adverse pregnancy
outcomes, and intra-amniotic infections.42 In this
study the abundance of Fusobacteria in the C-EB and EB groups was
significantly lower than the control group. Therefore, we cannot give a
reasonable explanation. At the genus level, the abundance of E.
coli / Shigella in the EB and C-EB groups was significantly lower than
the control group. E. coli / Shigella can cause watery diarrhea,
dysentery, and other symptoms.43 This means the
possibility of diarrhea and other symptoms is lower in the EB and C-EB
groups after delivery, which is an extremely interesting result. we do
not know the specific reason.