What is the MOST common trisomy in live-born humans?

Trisomy 21 (Down syndrome) is the most common trisomy in live-born infants, occurring in approximately 1 in 700 births. It is caused by nondisjunction during meiosis (95% of cases), Robertsonian translocation (4%), or mosaicism (1%). Oral findings include: macroglossia, fissured tongue, open mouth posture, Class III malocclusion, hypodontia, delayed eruption, and increased susceptibility to periodontal disease. Trisomy 16 is the most common trisomy in spontaneous abortions but is incompatible with live birth.