Various mechanical abnormalities in the cord can impede blood low and sometimes cause fetal harm. Of these, true knots are found in approximately 1 percent of births. hese form from fetal movement, and associated risks include hydramnios and diabetes (Hershkovitz, 2001; Raisanen, 2013). Knots are especially common and dangerous in monoamnionic twins, which are discussed in Chapter 45 (p. 874). When true knots are associated with singleton fetuses, the stillbirth risk is increased four-to tenfold (Airas, 2002; S0rnes, 2000).
Knots can be found incidentally during antepartum sonography, and a "hanging noose" sign is suggestive (Ramon y Cajal, 2006). hree-dimensional and color Doppler aid diagnostic accuracy (Hasbun, 2007). With these knots, optimal fetal surveillance is unclear but may include umbilical artery Doppler velocimetry, nons tress testing, or subjective fetal movement monitoring (Rodriguez, 2012; Scioscia, 201l). Allowing vaginal delivery is suitable, but abnormal intrapartum fetal heart rate tracings are more often encountered. hat said, cesarean delivery rates are not increased, and cord blood acid-base values are usually normal (Airas, 2002; Maher, 1996).
In contrast,alse knots form from focal redundancy and folding of an umbilical cord vessel. hese lack clinical signiicance.
Cord strictures are focal narrowings of the diameter that usually develop near the fetal cord insertion site (Peng, 2006). Characteristic pathological features include an absence of Wharton jelly and stenosis or obliteration of cord vessels at the narrow segment (Sun, 1995). In most instances, the fetus is stillborn (French, 2005). Even less common is a cord stricture caused by an amnionic band.
Cord loops are frequently encountered and are caused by coiling around various fetal parts during movement. A cord around the neck-a nuchal cord-is common, and vaginal delivery is suitable. One loop is reported in 20 to 34 percent of deliveries; two loops in 2.5 to 5 percent; and three loops in 0.2 to 0.5 percent (Kan, 1957; S0rnes, 1995; Spellacy, 1966).
During labor, up to 20 percent of fetuses with a nuchal cord have moderate to severe variable heart rate decelerations, and these are associated with a lower umbilical artery pH (Hankins, 1987). Cords wrapped around the body can have similar efects (Kobayashi, 2015). Despite their frequency, nuchal cords are not associated with greater rates of adverse perinatal outcome (Henry, 2013; Sheiner, 2006).
Last, a unic presentation describes when the umbilical cord is the presenting part in labor. These are uncommon and most often are associated with fetal malpresentation (Kinugasa, 2007). A funic presentation in some cases is identiied with placental sonography and color low Doppler (Ezra, 2003). Overt or occult cord prolapse can complicate labor. hus, once identiied at term, cesarean delivery is typically recommended.