Amniotic shelf

Last revised by Avni K P Skandhan on 3 Jun 2016

Amniotic shelf (also known as an amniotic sheet 4) refers to a sheet like projection that can result from uterine synechiae that has been encompassed by the expanding chorion and amnion. In contrast to amniotic bands, they are not thought to be associated with any fetal deformity. 

The estimated prevalence is at around 0.45-0.47% of pregnancies 5.

They are composed of four distinct layers: two layers of chorion sandwiched between two layers of amnion.

They may be are seen as shelf like thick bands and communicating along its entire length with the uterine wall, thus having a  base and a free edge. Color Doppler may demonstrate flow within the band. 

When large they can result in abnormal fetal presentations (e.g breech presentation) due to reduced fetal movement by compartmentalizing amniotic fluid 5.

Most amniotic sheets are considered benign (especially if they are incomplete 2). But there is some evidence that complete amniotic sheets may be associated with adverse fetal outcome2. Some authors suggest that perpendicular, in contrast to non-perpendicular, amniotic sheets are more commonly associated with a breech presentation at term 3.

If adjacent to the placenta on ultrasound consider:

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