Placentomegaly

Placentomegaly is a term applied to an abnormally-enlarged placenta.

Epidemiology

Associations

It can be associated with a number of maternal and fetal disorders which include:

• maternal
  • maternal anemia(s)
  • maternal diabetes
  • chronic intrauterine infections
  • alpha-thalassemia
• fetal
  • umbilical vein obstruction
  • fetal high output failure
  • fetal malformation
    • Beckwith-Wiedemann syndrome ^1,5
    • sacrococcygeal teratoma
    • hydrops fetalis and causative underlying conditions 
    • twin-to-twin transfusion syndrome ⁹
    • chromosomal anomalies
      • triploid: with an extra set from paternal origin
  • in utero infection ⁸
  • Finnish type congenital nephrotic syndrome ⁶
• fetomaternal hemorrhage
• placental abnormalities
  • placental chorioangioma
  • intraplacental hemorrhage
  • hydatidiform mole / partial mole
  • placental mesenchymal dysplasia
  • placental venous lakes

Radiographic features

Antenatal ultrasound

May show an increase in placental thickness and/or placental extent. The increase in size may be homo or heterogeneous dependent on the cause. The maximum thickness considered normal at any stage in pregnancy is often taken at 4 cm.

Differential diagnosis

The differential for an apparent increased in placental size on ultrasound includes:

• retroplacental hematoma: especially when it is isoechoic, e.g. from a placental abruption