Placenta and Umbilical Cord

This chapter discusses anatamical variations of placenta and umbilical cord. In some individuals, the placenta may be smaller than normal or excessively larger than normal. In 90% of individuals a discoid or oval-shaped placenta is seen. Abnormal shapes are seen in 10% of women and include notched or lobed placentas, membranous placentas, and other rare variants. Occasionally, more than one placenta may be found. The umbilical cord commonly connects to the main placenta. In general, the umbilical cord attaches to the center of the placenta. In 7% of placentas the umbilical cord is found to be attached to the edge of the placenta. Sometimes choroinic villi invade the whole uterine wall. This variant is placenta percreta. A single umbilical artery or a second umbilical vein are rare conditions. An incidence of 0.2% for a single umbilical artery has been reported. A single umbilical artery is seen more often in twins.