Yolk sac
Updates to Article Attributes
The yolk sac is the first anatomical structure identified within the gestational sac. It plays a critical role in embryonal development by providing nutrients, serving as the site of initial haematopoiesis, and contributing to the development of fetal gastrointestinal and reproductive systems 2.
Radiographic features
Ultrasound
Visualization
- yolk sac appears as a circular transonic mass within gestational sac
- yolk sac should be seen when the mean sac diameter (MSD) is 20 mm on transabdominal scanning and is usually seen endovaginally with an MSD of 8-10 mm.
-
visualization of a yolk sac is useful in distinguishing an intrauterine pregnancy (IUP) from a pseudogestational sac, a decidual cast cyst or an
anebryonicanembryonic pregnancy, as a yolk sac is only seen in an intrauterine pregnancy.A yolk sac should be seen when themean sac diameter (MSD)is 20 mm on transabdominal scanning and is usually seen endovaginally with an MSD of 8-10 mm.
In general if the MSD is ≥ 25 mm and no fetal pole or yolk sac can be identified on endovaginal scanning, then this suggests a failed pregnancy (anembryonic pregnancy).
In a normal early pregnancy, the diameter of the yolk sac should usually be <;6 mm while its shape should be near spherical.6
Visualisation of multiple yolk sacs is the earliest sign of a polyamniotic pregnancy, e.g twins.
Natural course
As the pregnancy advances, the yolk sac disappears and is often sonographically undetectable after 14-20 weeks.
Related pathology
-<p>The <strong>yolk sac</strong> is the first anatomical structure identified within the <a href="/articles/gestational-sac">gestational sac</a>. It plays a critical role in embryonal development by providing nutrients, serving as the site of initial haematopoiesis, and contributing to the development of fetal gastrointestinal and reproductive systems <sup>2</sup>. </p><h4>Radiographic features</h4><h5>Ultrasound</h5><p>Visualization of a yolk sac is useful in distinguishing an intrauterine pregnancy (IUP) from a <a href="/articles/pseudogestational-sac-1">pseudogestational sac</a>, a <a href="/articles/decidual-cast">decidual cast cyst</a> or an <a href="/articles/anembryonic-pregnancy">anebryonic pregnancy</a>, as a yolk sac is only seen in an intrauterine pregnancy.</p><p>A yolk sac should be seen when the <a href="/articles/mean-sac-diameter">mean sac diameter (MSD)</a> is 20 mm on transabdominal scanning and is usually seen endovaginally with an MSD of 8-10 mm.</p><p>In general if the MSD is ≥ 25 mm and no fetal pole or yolk sac can be identified on endovaginal scanning, then this suggests a <a href="/articles/non-viable-pregnancy">failed pregnancy</a> (<a href="/articles/anembryonic-pregnancy">anembryonic pregnancy</a>). </p><p>In a normal early pregnancy, the diameter of the yolk sac should usually be <<strong>6</strong> mm while its shape should be near spherical.</p><p>Visualisation of multiple yolk sacs is the earliest sign of a polyamniotic pregnancy, e.g twins.</p><h5>Natural course</h5><p>As the pregnancy advances, the yolk sac disappears and is often sonographically undetectable after 14-20 weeks.</p><h4>Related pathology</h4><ul>- +<p>The <strong>yolk sac</strong> is the first anatomical structure identified within the <a href="/articles/gestational-sac">gestational sac</a>. It plays a critical role in embryonal development by providing nutrients, serving as the site of initial haematopoiesis, and contributing to the development of fetal gastrointestinal and reproductive systems <sup>2</sup>. </p><h4>Radiographic features</h4><h5>Ultrasound</h5><ul>
- +<li>yolk sac appears as a circular transonic mass within gestational sac</li>
- +<li>yolk sac should be seen when the <a href="/articles/mean-sac-diameter">mean sac diameter (MSD)</a> is 20 mm on transabdominal scanning and is usually seen endovaginally with an MSD of 8-10 mm.</li>
- +<li>visualization of a yolk sac is useful in distinguishing an intrauterine pregnancy (IUP) from a <a href="/articles/pseudogestational-sac-1">pseudogestational sac</a>, a <a href="/articles/decidual-cast">decidual cast cyst</a> or an <a href="/articles/anembryonic-pregnancy">anembryonic pregnancy</a>, as a yolk sac is only seen in an intrauterine pregnancy.</li>
- +</ul><p>In general if the MSD is ≥ 25 mm and no fetal pole or yolk sac can be identified on endovaginal scanning, then this suggests a <a href="/articles/non-viable-pregnancy">failed pregnancy</a> (<a href="/articles/anembryonic-pregnancy">anembryonic pregnancy</a>). </p><p>In a normal early pregnancy, the diameter of the yolk sac should usually be <6 mm while its shape should be near spherical.</p><p>Visualisation of multiple yolk sacs is the earliest sign of a polyamniotic pregnancy, e.g twins.</p><h5>Natural course</h5><p>As the pregnancy advances, the yolk sac disappears and is often sonographically undetectable after 14-20 weeks.</p><h4>Related pathology</h4><ul>