Yolk sacs in twin pregnancy

The purpose of this study was to evaluate the relationship between the yolk sacs separated or not separated by septum and chorionicity twin pregnancies scanned early in the first trimester, and the relation between size and morphologic features of the yolk sac and the outcome of twin pregnancies.

In all 38 sets of twins two yolk sacs were identified. During the first trimester of a dichorionic twin pregnancy, the yolk sacs were always separated by a septum and not separated ("Eight" sign) in monochorionic twin pregnancy. In five cases, one of yolk sac was abnormally large (> 8 mm) and had thin wall. Four of the five mothers spontaneously aborted during the next 2-3 weeks. In one case of monochorionic twin ectopic pregnancy two yolk sacs were seen normally.

The sonographic identification of yolk sacs in multiple pregnancies allows an early and efficient recognition of presence and chorionicity of twin pregnancy, both in intra- and extrauterine. Identification of abnormal yolk sac or yolk sacs suggests death of one or all embryos.