True knots and false knots can form in the umbilical cord.
True knots occur in approximately 1% of pregnancies, with the highest rate occurring in monoamnionic twins. False knots (kinks in the umbilical cord vessels) are more common and have no known clinical significance.
True knots arise from fetal movements and are more likely to develop during early pregnancy, when relatively more amniotic fluid is present and greater fetal movement occurs. True knots are also associated with advanced maternal age, multiparity, and long umbilical cords.