Sonographic Evaluation of the Yolk Sac

Sonographic Evaluation of the Yolk Sac

Abstract

This pictorial essay aims to inform related clinicians by summarizing the normal and abnormal sonographic findings of the yolk sac in the first trimester of pregnancy. An abnormality in the sonographic appearance of a yolk sac can predict subsequent embryonic death or abnormalities. Therefore, the accurate recognition of normal and abnormal sonographic findings concerning the yolk sac can be used to anticipate the course of pregnancy.

The secondary yolk sac is the first extraembryonic structure that becomes sonographically visible within the gestational sac. During embryonic development, the yolk sac is the primary route of exchange between the embryo and the mother. The yolk sac also provides nutritional, immunologic, metabolic, endocrine, and hematopoietic functions until the placental circulation is established.1 Therefore, the yolk sac is crucial in early embryonic life.

The yolk sac is one of the most important conceptional structures evaluated sonographically in the first trimester. At present, the most important benefit of sonographic evaluation of the yolk sac is confirmation of an intrauterine pregnancy.1,2 It has been hypothesized that sonographic features related to the shape, size, and internal structure of the yolk sac can be associated with the gestational outcome.1,3

This pictorial essay aims to inform related clinicians by summarizing the normal and abnormal sonographic findings of the yolk sac during the first trimester of pregnancy.