Yolk sac calcification: a sonographic finding associated with intrauterine embryonic demise in the first trimester.

Two cases of the sonographic demonstration of yolk sac calcification associated with first-trimester intrauterine embryonic demise are reported. Histologic verification was obtained in one case. Yolk sac calcification may reflect typical dystrophic changes or be more specifically related to a yolk sac calcium-binding protein. Awareness of this sonographic finding--which the authors believe to be previously undescribed--may prevent diagnostic errors.