A true knot in the umbilical cord is an uncommon occurrence during pregnancy, where the cord forms a loop that tightens upon itself. This condition can potentially compromise the supply of oxygen and nutrients to the developing fetus. A true knot constricts significantly, posing a risk to fetal well-being. This rare phenomenon affects approximately 0.3% to 2% of all pregnancies.
Understanding a True Knot
A true knot in the umbilical cord develops when the fetus moves through a loop of the cord, causing it to tighten. This can occur early in pregnancy when the fetus has ample space to move within the amniotic sac. Unlike a true knot, a “false knot” is a common, harmless variation in the cord’s structure, often appearing as a localized thickening or bulge. These false knots are typically caused by an accumulation of Wharton’s jelly or a longer vessel, and they do not constrict blood flow.
The umbilical cord contains Wharton’s jelly, a gelatinous substance that surrounds and protects the umbilical arteries and vein. This jelly acts as a cushion, helping to prevent compression of the blood vessels. In many instances, Wharton’s jelly can prevent a true knot from tightening enough to cause problems. However, if the knot becomes sufficiently tight, this protective layer may not be enough to maintain adequate blood flow.
Factors Increasing Risk
Several factors can increase the likelihood of a true knot forming. Pregnancies involving identical twins, particularly monoamniotic-monochorionic twins who share the same amniotic sac, present a higher risk due to increased fetal movement and potential entanglement. Polyhydramnios, a condition with excessive amniotic fluid, is another contributing factor. This increased fluid volume provides the fetus with more space to move, increasing the chances of the cord looping and knotting.
A longer-than-average umbilical cord also contributes to a higher risk, as more cord length provides greater opportunity for entanglement. Umbilical cords typically measure around 50 to 60 centimeters at term; lengths significantly exceeding this range can be associated with increased knot incidence. Additionally, advanced maternal age, generally considered 35 years or older at delivery, may modestly increase the risk.
Potential Fetal Complications
When a true knot tightens, it can reduce or completely cut off the flow of blood, oxygen, and nutrients to the fetus. This diminished supply can lead to adverse effects on fetal development and well-being. Milder impacts may include slow fetal growth, also known as intrauterine growth restriction, where the fetus does not grow at the expected rate. Reduced fetal movement might also be observed due to compromised oxygen supply.
More severe complications arise from significant or prolonged oxygen deprivation, known as hypoxia. This can lead to serious outcomes such as brain damage, as the developing brain is highly sensitive to a lack of oxygen. In the most severe cases, where blood flow is completely obstructed for an extended period, a true knot can result in stillbirth. The severity of complications often depends on the knot’s tightness and the duration of compromised blood flow.
Diagnosis and Medical Management
Diagnosing a true knot before birth presents a notable challenge due to its variable nature and imaging limitations. While some knots may be incidentally observed during a routine ultrasound, it is generally difficult to definitively confirm their presence or assess their tightness. Consequently, true knots are often only diagnosed during labor or delivery, sometimes identified when changes in fetal heart rate patterns are detected through continuous monitoring.
Once a true knot is suspected or confirmed, medical management focuses on close monitoring of the fetal heart rate to detect signs of distress. There is no medical procedure to undo a true knot once it has formed in utero. If fetal distress, such as sustained abnormal heart rate patterns, indicates compromised oxygen supply, an emergency C-section may be performed for rapid and safe delivery. This proactive approach aims to mitigate potential complications from the knot’s tightening.