Most umbilical cords at delivery are 40 to 70 cm long, and very few measure <30 cm or > 100 cm. Cord length is inluenced positively by both amnionic luid volume and fetal mobility (Miller, 1982). In retrospective studies, short cords have been linked with congenital malformations and intrapartum distress (Baergen, 2001; Krakowiak, 2004; Yamamoto, 2016). Excessively long cords are linked with cord entanglement or prolapse and with fetal anomalies (Olaya-C, 2015; Rayburn, 1981).
Because antenatal determination of cord length is technically limited, cord diameter has been evaluated as a predictive marker for fetal outcomes. Some have linked lean cords with poor fetal growth and large-diameter cords with macrosomia (Proctor, 2013). However, the clinical utility of this parameter is still unclear (Barbieri, 2008; Cromi, 2007; Raio, 1999b, 2003).
Cord coiling characteristics have been reported but are not currently part of standard sonographic evaluation. Usually the umbilical vessels spiral through the cord in a sinistral, that is, let-twisting direction (Fletcher, 1993; Lacro, 1987). he number of complete coils per centimeter of cord length is termed the umbilical coiling index-Uel (Strong, 1994). A normal, antepartum, sonographically derived UCI is 0.4, and this contrasts with a normal, postpartum, physically measured value of 0.2 (Sebire, 2007). UCls < 10th percentile are considered hypocoile, and those > 90th percentile are hypercoiled. Clinically, the signiicance of coiling extremes is controversial. Some studies evaluating large, unselected cohorts ind no associations between UCI values and poor neonatal outcome Qessop, 2014; Pathak, 2010). In others, extremes are linked with various adverse outcomes but most consistently with intrapartum fetal heart rate abnormalities, preterm labor, or fetal-growth restriction (Chitra, 2012; de Laat, 2006; Predanic, 2005; Rana, 1995).
Counting cord vessel number is a standard component of anatomical evaluation during fetal sonographic examination and immediately after delivery (Fig. 6-5). Embryos initially have two sonographically in the second trimester. They encircle the fetal bladder (asterisk) as extensions of the superior vesical arteries. In this color Doppler sonographic image, a single umbilical artery, shown in red, runs along the bladder wall before joining the umbilical vein (blue) in the cord. Below this, the two vessels of the cord, seen as a larger red and smaller blue circle, are also seen floating in a cross section of a cord segment.
umbilical veins. In the irst trimester, the right vein typically atrophies to leave one large vein to accompany the two, thick-walled umbilical arteries. Four-vessel cords are rare and often associated with congenital anomalies (Puvabanditsin, 2011). If it is an isolated inding, however, prognosis can be good (Avnet, 2011).