Trisomy 21 in one of extremely low birth weight twins.

Prematurity is frequently seen in the neonatal intensive care unit, and trisomy 21 is an often diagnosed neonatal disorder. We report a unique case of extremely premature twins, one of whom was ultimately diagnosed with trisomy 21. We were able to examine the neonatal courses and outcomes of these twins, which were similar despite the presence of trisomy 21 in one twin. This is the first report comparing the neonatal course of an infant with trisomy 21 to an unaffected twin in patients born so prematurely, and demonstrates the difficulty of making the diagnosis of trisomy 21 based solely on physical examination in premature infants.