Small yolk sac

Last revised by Jeremy Jones on 20 Sep 2021

A small yolk sac is considered a non-specific feature and, at the time of writing, there are not many publications about the clinical importance of small yolk sacs.

According to some publications, a very small yolk sac may be a normal finding during early periods of normal embryologic development. However a distant study with certain limitations, suggests that a yolk sac diameter of 2 mm or less could be associated with failed early pregnancy when assessed at a gestational age of 8 to 12 weeks 1.

The yolk sac size begins to decrease during the late weeks of the first trimester.

This process is why gestational age should be taken into account when the size of the yolk sac is assessed. Some suggest that it may be prudent to perform serial sonographic examinations within a short period whenever a smaller-than-expected yolk sac is seen.

Practical points 

  • indeterminate abnormal yolk sac abnormality that should not be considered alone for the diagnosis of failed early pregnancy 
  • follow-up ultrasonography at 7-14 days to assess the pregnancy for viability is generally appropriate

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