Clinically Relevant Prenatal Ultrasound Diagnosis of Umbilical Cord Pathology

During embryogenesis, the four folds that emerge on the surface of the embryonic disc in the fourth embryonic week converge centrally in the umbilical area. The primitive umbilical ring is an oval reflection line between the amnion and embryonic ectoderm, which in the 5th week of the embryonic stage, passes the yolk duct and allantois together with the yolk vessels. The embryonic allantoid arteries form the umbilical arteries, and from the left allantoid vein, the umbilical vein is formed. The right umbilical vein that usually degenerates may persist as the single umbilical vein or the fourth vessel of the cord. The connection pedicle that consists of the allantois and umbilical vessels (two arteries and a vein), along with the yolk pedicle, passes through the canal that connects the intraembryonic and the extraembryonic cavities. Subsequently, being covered by the amnion, the pedicles form the primitive umbilical cord [1]. The rapid growth of the intestine and liver in the 6th week of embryologic development causes a temporary inadequacy of the abdominal cavity for its contents; as a repercussion, there is an intestinal protrusion in the extraembryonic residual coelom, at the base of the umbilical cord. At the end of the first trimester, the yolk sac located in the chorionic cavity degenerates; thus, physiological herniated intestinal loops resolve after 12 weeks of gestation [2,3]. Subsequently, the umbilical cord vessels remain just surrounded by Wharton’s jelly, a mucoid matrix of mesodermal origin. Umbilical arteries present a helical disposition around the vein, forming tortuosities and false nodes. 

Umbilical cord anomalies (UCA) are not rare and are often associated with structural or chromosomal abnormalities, fetal intrauterine growth restriction, and poor pregnancy outcomes due to prematurity and placentation deficiency. The NICHD Stillbirth Collabora- tive Research Network Group reported in 2020 that, from 496 stillbirths wherein cause of death was analyzed and documented using the INCODE (Initial Causes of Fetal Death) classification system, 19% of deaths were due to umbilical cord abnormalities: a total of 27% by umbilical cord knots, torsions or stricture; 29% by nuchal, shoulder or body umbilical cord entanglement; and 5% were complicated by umbilical cord prolapse [4].

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