**4.2. Umbilical vein varix**

Vasa previa

It is important to be aware that velamentous cord insertion is associated with an increased rate of vasa previa. Vasa previa is a form of velamentous cord insertion in which velamentous vessels pass through the fetal membranes of the lower uterine segment and incidence is estimated to be 0.04% [35]. These fetal vessels may break when membrane rupture occurs and the

A hypoplastic umbilical artery has a smaller diameter than the contralateral artery, showing by ultrasonography an artery-to-artery diameter difference of more than 50% [37] (**Figure 7**). It seems that the hypoplastic umbilical artery represents a mild form of the single umbilical artery. Described anomalies include trisomy 21, polyhydramnios, congenital heart disease, stillbirth, trisomies, and fetal growth restriction. The presence of discordant umbilical arteries is a sign of different umbilical artery blood flow indices and of placental disease [38]. This condition increases the risk of IUGR, placental infarction, umbilical cord hematoma, and abnormal umbilical cord insertion. It is also known that the fetal prognosis is better for hypoplastic

Karyotyping is not indicated in isolated hypoplastic umbilical artery because there is no evi-

result is fetal exsanguination. Intrapartum diagnosis is very difficult in this case [36].

**4. Abnormal structure or configuration of vessels**

umbilical arteries compared with SUA syndrome [37].

dence of increased risk of chromosomal defects.

**Figure 7.** Hypoplastic umbilical artery.

**4.1. Hypoplastic umbilical artery**

352 Congenital Anomalies - From the Embryo to the Neonate

Umbilical vein varix is a rare condition which occurs in the intrahepatic portion of the umbilical vein presents an incidence of 2.8:1000 [39]. Ultrasound scan usually discovers a circular vessel dilation ≥ 9 mm, 59 or more than 50% over the diameter of the intrahepatic UV [40]. The condition is associated with chromosomal anomalies in up to 12% of cases, especially trisomy 21and poor fetal outcome with emergent cesarean delivery [41].

Complete follow-up includes karyotyping, regular fetal testing, and third trimester interval growth studies [42]. Because the incidence is very low, the clinical significance remains controversial.
