trisomy 18 (MONDO_0018071) is a chromosomal abnormality associated with the presence of an extra chromosome 18 and characterized by growth delay, dolichocephaly, a characteristic facies, limb anomalies and visceral malformations. Also known as: E3 trisomy, Edwards syndrome, chromosome 18 duplication, complete trisomy 18 syndrome, trisomy type 18.