**1. Introduction**

The umbilical cord is an anatomical structure composed of two arteries and a vein covered by Wharton's jelly derived from allantois, which in turn is upholstered by a layer of amniotic coating [1]. The umbilical cord connects the foetus and the placenta and ensures adequate nutrition, foetal oxygenation, and proper waste elimination. The integrity of the maternal-foetal circulation is essential for the correct development and survival of the foetus. If foetal oxygenation is compromised, foetal hypoxia can affect essential systems such as the cardiovascular system or the central nervous system. Abnormalities

**Citation:** Sánchez-Trujillo, L.;

García-Montero, C.; Fraile-Martinez, O.; Guijarro, L.G.; Bravo, C.; De Leon-Luis, J.A.; Saez, J.V.; Bujan, J.; Alvarez-Mon, M.; García-Honduvilla, N.; et al. Considering the Effects and Maternofoetal Implications of Vascular Disorders and the Umbilical Cord. *Medicina* **2022**, *58*, 1754. https://doi.org/10.3390/ medicina58121754

Academic Editors: Marius L. Craina and Elena Bernad

Received: 21 October 2022 Accepted: 22 November 2022 Published: 29 November 2022

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**Copyright:** © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

or complications that affect these functions involve foetal and neonatal compromise and increase perinatal morbidity and mortality [2].

Both umbilical arteries arise from the internal iliac arteries and are responsible for returning deoxygenated blood from the foetus to the mother. The two arteries converge in the chorionic arteries of the placenta, and their position in the cord is variable. At the histological level, they are characterized by a small lumen comprising a muscular middle layer and an external circular layer and lacking an internal elastic lamina. There is a variant called the single umbilical artery in which there is only one umbilical artery, which can be the result of aneuploidies or congenital anomalies or simply an incidental finding.

The umbilical vein results from the convergence of the chorionic veins and is responsible for the supply of oxygenated blood to the foetus. It is characterized by a wider lumen, with an internal elastic limiting layer and a lax muscular layer in a circular arrangement. During embryogenesis, a right umbilical vein develops that normally degenerates during embryonic development but can persist as a variant in the form of a supernumerary vessel. The umbilical vein connects with the systemic circulation of the foetus through the ductus venosus, which drains into the inferior vena cava. When the cord is detached after birth, the structures contained in the cord sheath remain at the base. The closed blood vessels remain permeable during the first weeks of life. Finally, the umbilical arteries will be defined at the lateral umbilical ligaments, the umbilical vein at the round ligament, and the ductus venosus at the ligamentum venosus.

Wharton's jelly is derived from mesoblastic cells of the embryonic pedicle and is composed of a hydrophilic extracellular matrix that is rich in water, proteoglycans, and hyaluronic acid. Wharton's jelly provides supportive and protective functions against compression.

The umbilical cord usually inserts in the placenta centrally or eccentrically, which is considered a normal cord insertion. However, there are insertion abnormalities such as marginal insertion, velamentous insertion, or vasa praevia [1].

Velamentous insertion of the umbilical cord consists of the divergence of umbilical vessels, unsupported by the umbilical cord or placental tissue, as they traverse amnion and chorion before reaching the placenta [3]. It is characterized by the presence of membranous umbilical vessels in the region of placental insertion, little Wharton jelly and susceptibility to compression with the danger of hemorrhage and fetal exsanguination. Vasa praevia consists of an anomaly of the umbilical vessels that cross the membranes of the low uterine segment, unsupported by umbilical cord or placental tissue, with a high risk of rupture of the vessels [3].

Ultrasound examination of the umbilical cord can be performed from the eighth gestational week and is key during prenatal follow-up [4]. There is no consensus about umbilical cord examination among the different societies' guidelines. The International Society of Ultrasound in Obstetrics and Gynecology, do not recommend checking specifically for possible umbilical cord abnormalities [5]. However, the American Institute of Ultrasound in Medicine (AIUM) guidelines highlight the importance of umbilical cord ultrasound examination between second and third-ultrasound examinations [4].At the anatomic level, its foetal and placental insertion, number of vessels, length, diameter, coiling, and vascular anomalies are important [4].

The average thickness of the cord varies and depends on the length of gestation. A cord with a diameter of less than 1 cm is considered thin [6].

The length of the cord is variable between sexes and gestational age; in term gestations, cords shorter than 35 cm are considered short, and those longer than 70 cm are considered long [6].

Coiling corresponds to the winding pattern of the umbilical arteries around the umbilical vein; 1–3 coils per 10 cm of length is considered normal [1]. In most cases, the pattern is to the left and is evaluated by calculating the coiling index (inverse of the distance separating two spiral turns).

Correct foetal growth and development are also determined by correct placental development. Dysregulation of cell differentiation during placental angiogenesis implies an alteration in the primitive foetal circulation, which may indicate abnormal intrauterine growth [7]. The perinatal and neonatal implications of incorrect placental development vary greatly depending on its severity.

Several factors have been linked to changes in foetal blood flow, including the presence of vascular alterations during pregnancy, which in turn encompass anomalies and vascular alterations in the umbilical cord [8].
