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. Colour 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:
- 1. Korbin CD, Benson CB, Doubilet PM. Placental implantation on the amniotic sheet: effect on pregnancy outcome. Radiology. 1998;206 (3): 773-5. Radiology (abstract) - Pubmed citation
- 2. Tan KB, Tan TY, Tan JV et-al. The amniotic sheet: a truly benign condition? Ultrasound Obstet Gynecol. 2005;26 (6): 639-43. doi:10.1002/uog.1994 - Pubmed citation
- 3. Lazebnik N, Hill LM, Many A et-al. The effect of amniotic sheet orientation on subsequent maternal and fetal complications. Ultrasound Obstet Gynecol. 1996;8 (4): 267-71. doi:10.1046/j.1469-0705.1996.08040267.x - Pubmed citation
- 4. Stamm E, Waldstein G, Thickman D et-al. Amniotic sheets: natural history and histology. J Ultrasound Med. 1991;10 (9): 501-4. J Ultrasound Med (abstract) - Pubmed citation
- 5. Nyberg DA, McGahan JP, Pretorius DH. Diagnostic imaging of fetal anomalies. Lippincott Williams & Wilkins. (2003) ISBN:0781732115. Read it at Google Books - Find it at Amazon