Abstract
Background
Nonmosaic Trisomy 9 is a rare chromosomal abnormality, accounting for approximately 2.2%–2.7% of spontaneous abortions caused by autosomal trisomies, and is characterized by a heterogeneous multisystem phenotype and an extremely poor prognosis. Prenatal imaging may demonstrate severe multisystem abnormalities; however, these findings are not specific to Trisomy 9, making cytogenetic testing essential for definitive diagnosis. We report a case of prenatally diagnosed apparently nonmosaic Trisomy 9 in which diagnosis enabled individualized perinatal care.
Case
A 44‐year‐old multiparous woman was referred to our hospital at 25 weeks’ gestation because of severe fetal growth restriction and multiple structural anomalies. Amniocentesis at 28 weeks’ gestation demonstrated 47,XY,+9 in all 100 examined colonies, consistent with apparently nonmosaic Trisomy 9. Following multidisciplinary counseling and shared decision‐making, an individualized birth plan was developed. The family wished to avoid aggressive life‐prolonging interventions while prioritizing the opportunity to meet their infant alive; therefore, fetal monitoring, cesarean delivery for fetal indications, and mask ventilation without further resuscitation were incorporated into the plan. Emergency cesarean delivery was performed at 36 weeks and 2 days for nonreassuring fetal status. The infant died approximately 9 h after birth while receiving family‐centered palliative care.
Conclusion
This case highlights the clinical importance of definitive prenatal cytogenetic diagnosis in apparently nonmosaic Trisomy 9, enabling phenotype‐informed prognostic counseling and individualized perinatal management.