![]() ![]() Unlike the risk for autosomal trisomies, the risk for polyploidies and for monosomy X (Turner syndrome) does not increase 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. Autosomal trisomies result from maternal meiotic nondisjunction of gametogenesis and the risk increases with maternal age. 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%). The majority (90%) of these chromosomal anomalies are numerical, particularly autosomal trisomies (involving chromosomes 13,16, 18, 21, 22), polyploidy and monosomy X. Chromosomal anomalies are responsible for more than 50% of spontaneous abortions. First trimester spontaneous abortions occur in 15 to 20% of all clinically recognized pregnancies.
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