how to measure yolk sac on ultrasound
In a normal early pregnancy, the diameter of the yolk sac should usually be <6 mm while its shape should be near spherical. A yolk sac â¥6 mm is suspicious for a failed pregnancy, but not diagnostic. Visualisation of multiple yolk sacs is the earliest sign of a polyamniotic pregnancy, e.g. twins.
The number of yolk sacs matches the number of amniotic sacs if the embryos are alive 6. As the pregnancy advances, the yolk sac progressively increases from the 5th to end of the 10th gestational week, following which the yolk sac gradually disappears and is often sonographically undetectable after 14-20 weeks.