Introduction
Fetal echogenic bowel (FEB) refers to the ultrasound images of the fetal intestine, which are similar to or stronger than the echo of adjacent bone. 1 FEB is one of the soft indices of fetal chromosomal abnormalities. Between 0.2% and 1.8% of fetuses have this sign in the second trimester of pregnancy based on an ultrasound examination.2-3 Most fetuses with FEB have a good outcome, but some fetuses have an underlying pathologic condition, including chromosomal abnormalities, cystic fibrosis (CF), intrauterine growth restriction (IUGR), and intrauterine cytomegalovirus.4 However, The mechanism of FEB is unclear. Some studies suggest that meconium may be caused by fetal intestinal mucus, intestinal gas, and ingestion of amniotic fluid.5-8
The traditional belief has always been that the fetus is sterilein utero .9 With the development of modern sequencing technology, more and more evidence has shown that the fetus is colonized in utero . Collado et al.10reported a low abundance microbiome in the amniotic fluid and placenta. Several research teams have shown that bacteria not only exist in the fetal environment of healthy term pregnancies, but also constitute the placental microbiota that participate in normal fetal development and initiate colonization of the fetal microbiota.11-14 de Goffau et al.15 concluded that the microbiota is transferred between the maternal and fetal interface. Martinezka et al.16 found that there are rich and diverse bacterial DNA in mouse embryo guts. The bacterial DNA is transferred from the maternal microbiota to the fetal gut and may be the key stimulating factor to promote normal development of fetal mucosal immunity. A recent radioimmunoassay study showed the presence of culturable bacteria in the fetal gut in the second trimester.17 Such evidence indicates that colonization of human intestinal flora begins in the fetal period.
In recent years, a number of studies have shown that several diseases during the fetal period are related to intestinal flora. Guzzardi et al.18 found that growth of the fetal heart is associated with colonization of the intestinal flora in utero . Zhang et al.19 found that the diversity of the intestinal flora in newborn piglets with IUGR was decreased. Therefore, we propose a hypothesis that hyperechogenic bowel may be related to intestinal flora via mucus and gas. The purpose of this study was to determine the intestinal flora of neonates using high-throughput sequencing technology, as well as the relationship between hyperechogenic bowel and intestinal flora.