Trisomy 13, 18, 21, Triploidy and Turner syndrome: the 5T’s. Look at the hands

First trimester spontaneous abortions occur in 15 to 20% of all clinically recognized pregnancies. Chromosomal anomalies are responsible for more than 50% of spontaneous abortions. The majority (90%) of these chromosomal anomalies are numerical, particularly autosomal trisomies (involving chromosomes 13,16, 18, 21, 22), polyploidy and monosomy X. At birth chromosomal anomalies are still an important cause of congenital malformations occurring in 0,55% of newborns (autosomal: 0,40%, sex chromosomal: 0,15%). Autosomal trisomies result from maternal meiotic nondisjunction of gametogenesis and the risk increases with maternal age. Polyploidy (triploidy (3n = 69) or tetraploidy (4n = 92)), results from a contribution of one or more extra haploid chromosome sets at fertilization. Unlike the risk for autosomal trisomies, the risk for polyploidies and for monosomy X (Turner syndrome) does not increase with maternal age. In the prenatal period the ultrasonographic diagnosis of some autosomal trisomies such as trisomy 13 and 18 is feasible based on the frequently seen major malformations while the diagnosis of trisomy 21 often remains challenging due to the absence of major malformations in > 50% of cases. For Turner syndrome (monosomy X), the lethal form will present with cystic hygroma colli and hydrops but the non lethal form is difficult to recognize by ultrasound in the second trimester. The 5 frequently encountered chromosomal anomalies (Trisomy 13, 18, 21, Turner syndrome and Triploidy) referred here as the 5T’s have specific hand features which will be discussed.