Patau syndrome (trisomy 13) is a genetic condition resulting from the presence of three (rather than the usual two) copies of chromosome 13. It has varied clinical features, commonly including intrauterine growth retardation, microcephaly, cardiac defects, small or absent close-set eyes and extra fingers. It is a severe condition that often results in stillbirth or death in infancy.

Edwards syndrome (trisomy 18) is a severe, multi-system genetic condition resulting from the presence of three (rather than the usual two) copies of chromosome 18. It is often identified during prenatal screening, but may present postnatally.

Down syndrome (trisomy 21) is a genetic condition caused by the presence of three (rather than the usual two) copies of chromosome 21. It is often identified during prenatal screening, but may present at birth or in early childhood.

In around 2%–5% of couples who experience recurrent miscarriage, there is a genetic cause. This is most commonly a balanced structural chromosomal anomaly, often a balanced translocation.