Fetal sex discordance in a monochorionic twin pregnancy following intracytoplasmic sperm injection: A case report of chimerism and review of the literature.

A 39-year-old woman who became pregnant with twins after an intracytoplasmic sperm injection was referred at the ninth gestational week to determine chorionicity. Ultrasonographic examination showed a monochorionic diamniotic twin pregnancy. First trimester nuchal translucency measurements of the fetuses were 1.6 and 2.7 mm. A non-invasive prenatal test was performed and revealed low risk. One fetus appeared to be female and the other male at the 14th gestational week. Second trimester anatomic scanning results were otherwise normal for both fetuses. The newborns delivered at term appeared to be normal female and male babies phenotypically. At the fourth month, buccal cell analysis showed chimeric karyotypes, 46,XX[98]/46,XY[2] and 46,XY[98]/46,XX[2] in the female and male infant, respectively. The recognition of sex discordance despite monochorionicity may be a clue for the diagnosis of such rare cases of chimerism in dizygotic twins, most of which occur in pregnancies obtained by assisted reproductive technology.