At the upper left is a so-called "accessory lobe" or succenturiate lobe of placenta. This is a twin placenta. Such accessory lobes by themselves are of no major consequence unless large with tenuous blood supply,
but they could produce problems at the time of delivery.
A succenturiate (accessory) lobe is a second or third placental lobe that is
much smaller than the largest lobe. Unlike bipartite lobes, the smaller
succenturiate lobe often has areas of infarction or atrophy. The risk factors
associated are advanced maternal age, primigravida, proteinuria in the first
trimester of pregnancy, and major malformations in the fetus. The membranes
between the lobes in such placenta can be torn during delivery, and the extra
lobe can be retained after rest of the placenta has been delivered, with
consequent postpartum bleeding.