Predisposing factors in the formation of true knots of the umbilical cord-analysis of morphometric and perinatal data

Fifty-four umbilical cords with a true knot were analysed and compared to 108 normal cords. True knots were found in 1.22% of births. They occurred at a significantly higher rate in longer cords (P less than 0.00001), in male fetuses (P less than 0.05) and in multiparous women (P less than 0.003). Signs of fetal distress were observed more frequently in female fetuses, especially in those with longer cords. A true knot seems to disrupt the significant correlation (P less than 0.007) between cord length and birth weight that we observed in controls. The present study reviews the literature on the subject and suggests a possible mechanism for true knot formation.