ECHOGENIC AMNIOTIC FLUID

Amniotic fluid is a mixture of:

• Urine.
• Fluid from the fetal lung.
• Saliva.
• Cellular debris from the skin (and its glands), the lung, kidney, transitional epithelium from the fetal genitourinary tract.
• Meconium from the fetal colon may be present in late gestation.

ECHOGENIC AMNIOTIC FLUID PRIOR TO 24 WEEKS

• Intraamniotic bleed.
• Blister forming skin disorders.

ECHOGENIC AMNIOTIC FLUID AFTER 24 WEEKS

• Cellular debris (vernix caseosa) - the amount of cellular debris may be considerable and may render the amniotic fluid opaque to the ultrasound beam. This cellular debris is most apparent immediately after fetal movement when it may be seen to swirl around and then settle once again to the dependent portion of the uterus (1). There is a vague relationship between the amount of cellular debris and fetal maturity.

• Ichthyosiform dermatoses.
• Meconium stained amniotic fluid.
• Intraamniotic blood (amniocentesis or fetal skin lesions).
• Blister forming skin disorders.

In a recent study (2) the causes of third trimester echogenic fluid was:

• Vernix (95%).
• Meconium (5%).

It has been suggested that layering of echoes may be a sign of meconium as opposed to vernix (3), however this is an unreliable sign (2). The layering effect has been reported with vernix (4), and evenly distributed particles have been described with meconium (5).

REFERENCES

1. Manning FA (ed). Fetal medicine. Principles and practice. Appleton and Lange, Norwalk, Connecticut 1995:185-187.
2. Brown DL, Polger M, Clark PK et.al. Very echogenic amniotic fluid: Ultrasonography-amniocentesis correlation. J Ultrasound Med 1994;13:95-97.
3. Benacerraf BR, Gatter MA, Ginsburgh F. Ultrasonographic diagnosis of meconium-stained amniotic fluid. Obstet Gynecol 1984;149:570.
4. Sepulveda WH, Quiroz VH. Sonographic detection of echogenic amniotic fluid and its clinical significance. J Perinat Med 1989;17:333.
5. Sherer DM, Abramowicz JS, Smith JA et.al. Sonographically homogeneous echogenic amniotic fluid in detecting meconium-stained amniotic fluid. Obstet Gynecol 1991;78:819.