Abstract
Cystic hygroma of the neck was observed in seven spontaneously aborted, severely autolyzed female fetuses. Four of five karyotyped cases had the 45,XO karyotype; one was a normal female, 46,XX. Diagnostic features associated with monosomy X in fetuses, which were observed in six of these cases, include large cystic hygromas, generalized edema, edematous chorionic villi with scalloped borders and trophoblastic inclusions, and, possibly, a small heart. In contrast, the single euploid fetus in this series had a small cystic hygroma, no hydrops, and chorionic villi of normal size. These features may differentiate cystic hygromas associated with the XO karyotype, which are not associated with recurrence risk, from those associated with a familial syndrome.