Placental thickness

Placental thickness tends to gradually increase with gestational age in a linear fashion. Sonographically, this can be seen to be approximately 1 mm per week and the thickness of the placenta can be used to approximate gestational age:

  • approximate gestational age (in weeks) = placental thickness +/- 10 mm

The maximum thickness of a normal placenta at any point during pregnancy is often taken considered to be 4 cm 3. Anterior placentas are ~0.7 cm thinner than posterior placentas and maximum thickness for an anterior placenta is ~3.3 cm 7.

Increased thickness

An abnormally increased placental thickness falls under the spectrum of placentomegaly. This can happen with number of conditions and is associated with increased risk of placental insufficiency. Causes include:

If the placenta is thickened and contains cysts, then other entities should be considered.

An important mimic for a thickened placenta is an isoechoic abruption.

A transient myometrial contraction can also mimic a thickened placenta.

Decreased thickness

An abnormally decreased placental thickness can be seen seen with:

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Article Information

rID: 13571
Section: Approach
Tag: cases
Synonyms or Alternate Spellings:
  • Thickness of the placenta

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