True knots can form in the umbilical cord. True knots occur in approximately 1% of pregnancies, with the highest rate occurring in monoamnionic twins. 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.
Image by Jian-Hua Qiao, MD, FCAP, Los Angeles, CA, USA. (source: flickr)
True knots have been reported to lead to a 4-fold increase in fetal loss, presumably because of compression of the cord vessels when the knot tightens. (adapted from emedicine)Other similar posts