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 gastrointestinalfetal gastrointestinal and reproductive systems 2.
Radiographic assessmentfeatures
Ultrasound
VisualisationVisualization of a yolk sac is is useful in distinguishing an intrauterine pregnancy (IUP) from a pseudogestational sac, a decidual cast cyst or a blighted ovumanebryonic pregnancy, as it isa yolk sac is only seen in the formeran intrauterine pregnancy.
A yolk sac should always be seen when the mean sac diameter (MSD)
- is 20 mm on
trans-abdominaltransabdominal scanningand -
and is usually seen
trans-vaginallyendovaginally with an MSD of 8-10 mm.
In general if the MSD is 25 mm or greater and no fetal pole or yolk sac can be identified on trans-vaginalendovaginal scanning, then this suggests a non-viablefailed 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.
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 not detectable after 14-20 weeks.
See also
-<p>The <strong>yolk sac</strong> is 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 gastrointestinal and reproductive systems <sup>2</sup>. </p><h4>Radiographic assessment</h4><h5>Ultrasound</h5><p>Visualisation of a yolk sac is useful in distinguishing an intrauterine pregnancy (IUP) from a <a href="/articles/pseudo-gestational-sac">pseudogestational sac</a>, a <a href="/articles/decidual-cast">decidual cast cyst</a> or a <a href="/articles/anembryonic-pregnancy">blighted ovum</a>, as it is only seen in the former.</p><p>A yolk sac should always be seen when the <a href="/articles/mean-sac-diameter">mean sac diameter (MSD)</a> is 20 mm on trans-abdominal scanning and usually seen trans-vaginally with an MSD of 8-10 mm.</p><p>In general if the MSD is 25 mm or greater and no fetal pole or yolk sac can be identified on trans-vaginal scanning then this suggests a <a href="/articles/non-viable-pregnancy">non-viable 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 not detectable after 14 weeks.</p><h4>See also</h4><ul><li><a href="/articles/irregular-yolk-sac">irregular yolk sac</a></li></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><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 a <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></p><ul>
- +<li>is 20 mm on transabdominal scanning</li>
- +<li>and is usually seen endovaginally with an MSD of 8-10 mm</li>
- +</ul><p>In general if the MSD is 25 mm or greater 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 not detectable after 14-20 weeks.</p><h4>See also</h4><ul>
- +<li><a href="/articles/irregular-yolk-sac">irregular yolk sac</a></li>
- +<li><a href="/articles/calcified-yolk-sac">calcified yolk sac</a></li>
- +</ul>
References changed:
- 1. N Gupta and TL Angtuaco "Embryosonology in the First Trimester of Pregnancy" Ultrasound Clinics 2 (2007) 175-185. http://dx.doi.org/10.1016/j.cult.2007.07.006
- 1. N Gupta and TL Angtuaco "Embryosonology in the First Trimester of Pregnancy" Ultrasound Clinics 2 (2007) 175-185
Tags changed:
- first trimester
- abr certifying ultrasound