Bilobed placenta

A bilobed placenta also referred to as bipartite placenta, is a variation in placental morphology and refers to a placenta separated into two near equal-sized lobes. If more than two lobes are present, it is termed a trilobed, four-lobed and so on. If the second lobe is smaller than the main lobe (with the umbilical cord insertion), then the smaller lobe is termed a succenturiate lobe.

Epidemiology

The estimated incidence is at up to ~4% of pregnancies.

Pathology

It is thought to result from localized placental atrophy as a result of poor dedicualisation or vascularization of a part of the uterus (dynamic placentation theory) ⁵.

Associations

• velamentous insertion of the cord

Radiographic features

Antenatal ultrasound

May be sonographically seen as two separate placental discs of nearly equal size. The cord usually attaches to a thin connecting rim of chorionic tissue which bridges the two lobes. Less commonly the cord may insert into one of the lobes.

Complications

• it carries an increased incidence of type II vasa previa
• it may increase the incidence of postpartum hemorrhage due to retained placental tissue

Differential diagnosis

If more than one lobe of the placenta is seen in an antenatal scan consider:

• succenturiate lobe: accessory lobe(s) smaller in size than the main lobe
• twin pregnancy with two placentas