A succenturiate placenta has one or more accessory lobes connected to the main placenta by the amnion and chorion. Fetal vessels run through the connecting membranes supplying the accessory lobe from the main placenta. The incidence of succenturiate placentas varies between 0.16% and 3% of pregnancies.
An accessory placental lobe is rarely diagnosed antenatally. However, sonographer/ sonologist awareness of this potential placental abnormality will increase the likelihood of detection. If undetected a succenturiate lobe may be retained inutero after delivery, resulting in postpartum hemorrhage. More importantly, if the connecting vessels between the main placenta and the accessory lobe traverse the internal cervical os, fetal exsanguination may occur at the time of membrane rupture.
An accessory placental lobe may occasionally be confused with a uterine contraction. Color Doppler helps to detect the fetal vessels that run through the connecting membranes to the accessory lobe.
An accessory lobe is usually smaller, but it may equal the main placental mass.
The umbilical cord insertion into the placenta identifies the main body of the placenta.
A bilobate placenta, in contrast to a succenturiate lobe, has two nearly equal sized lobes.
The umbilical cord of a bilobate placenta inserts into the membranes between the lobes.