Twin pregnancy with Roberts syndrome in one fetus and trisomy 18 in the other.

We report a case of a 26-year-old multigravida pregnant woman with a history of 3 stillbirths with hydrops fetalis who presented with 17 weeks menstrual age. Sonographic examination revealed twin gestation. Twin 1 showed subcutaneous edema, pleural effusion, and mesomelic limb shortening, suggestive of lethal skeletal dysplasia (Roberts syndrome). Twin 2 corresponded to 17 weeks menstrual age with no major malformations. Karyotyping of the fetuses showed normal karyotype in twin 1 and trisomy 18 in twin 2. Fetal autopsy confirmed the sonographic findings. The occurrence of trisomy 18 in the fetus may be due to chance, but it raises the possibility that the heterozygotes of Roberts syndrome may be at higher risk of nondisjunction and aneuploidy in the fetus. Furthermore, this case illustrates that karyotyping of both fetuses is warranted when 1 of the twins is found to have major malformations.