Third trimester intrauterine fetal death caused by arterial aneurysm of the umbilical cord.

Umbilical artery aneurysm (UAA) of the umbilical cord is an extremely rare lesion, with only 8 reported cases in the English-language literature; 7 of these were associated with significant fetal morbidity or mortality and 4 were associated with fetal trisomy 18. We report an additional case of UAA with normal karyotype that resulted in intrauterine growth restriction and fetal demise. It has been suggested that these aneurysms cause fetal hypoxia and intrauterine fetal death, either by compression of the umbilical vein or by acute kinking of the umbilical cord. Cytogenetic analysis should be performed in all cases diagnosed with this unusual lesion, and placental mosaicism for trisomy 18 should be excluded.