A rare case of heterokaryotypic monozygotic monochorionic twin pregnancy is presented, highlighting the importance of detailed sonographic evaluation, dual sac amniocentesis, and zygosity determination in diagnosing and managing such cases. This case report emphasizes the need to recognize heterokaryotypia, as it significantly impacts prenatal and postnatal outcomes, often leading to dual fetal loss. The patient, a 28-year-old gravida 2 para 1, conceived a monochorionic diamniotic twin pregnancy spontaneously. Initial sonographic findings revealed nuchal edema in one fetus, progressing to a huge septated cystic hygroma, which eventually led to fetal hydrops. Karyotype analysis revealed a discordant genetic makeup between the twins, with one fetus having pure Turner syndrome (45,XO) and the other a variant Turner syndrome (46Xdel(X)(p11)). The couple opted for conservative management, but the pregnancy was complicated by advanced labor at 23 weeks, resulting in the abortion of both fetuses. The case underscores the necessity of comprehensive prenatal assessment and management strategies for monochorionic twin pregnancies, especially when genetic abnormalities are suspected. The potential for selective fetal reduction and the importance of accurate zygosity determination are discussed, emphasizing the need for further research and clinical guidelines in this rare but significant condition.
