2010-10-18-10 Bilobate placenta © Freddy www.TheFetus.net
Bilobate placenta is an abnormality in which two placental lobes are separated by a segment of membranes. It is present in 2% to 8% of all placentas. The umbilical cord may insert on either of the lobes or in a velamentous fashion, in between the lobes. The latter is the most common arrangement.
If there is an obvious size discrepancy between the lobes, one lobe is much smaller than the other, we call this finding placenta with an accessory (succenturiated) lobe.
Multilobed placentas are thought to arise due to an implantation in areas of decreased uterine perfusion. An example is a lateral implantation in between the anterior and posterior walls of the uterus with one lobe on the anterior and one on the posterior wall. Other local factors leading to multilobation are implantation over leiomyomas or in areas of previous surgery.
It's always necessary to exclude presence of vasa previa and thrombosis of the membranous vessels connecting the two lobes.
Bilobate placentas and succenturiate lobes are associated with antenatal bleeding, placenta previa, retained placenta and vasa previa.
Each lobe should be examined individually. The integrity of the membranous vessels connecting the lobes should be evaluated. It is recommended to search for signs of hemorrhage into the adjacent membranes. In case membranous vessels are present and associated with thrombosis, rupture, or hemorrhage into the membranes, the possibility of fetal hemorrhage should be considered.
Following images show two cases of bilobate placenta diagnosed at 23-year-old G1 P0 with unremarkable history. No other pathology was found in both of the cases.
Images 1,2: Images show anterior and posterior uterine wall with anterior (*) and posterior (**) placental lobes. Note that both lobes are of an equal size, contrary to succenturiate lobe.
Images 3,4: Images show power Doppler demonstrating vascularization of placental lobes and umbilical cord.
Images 1,2: Images of the anterior (*) and posterior (**) placental lobes.
Images 3,4,5: Doppler imaging showing umbilical cord insertion on the posterior placental lobe.