Humans have 23 pairs of chromosomes (46 in total), which are strands of DNA and proteins containing the genetic information necessary for the structure and function of the body.

Chromosomal abnormalities are conditions where the number and/or structure of chromosomes differ from the normal arrangement. Trisomies, in particular, occur where three copies of a chromosome are present instead of the usual two. For example, Trisomy 21 involves three copies of chromosome 21 and is associated with Down syndrome.

Early detection of a chromosomal abnormality enables future parents to plan appropriate obstetric and gynaecological management during pregnancy and childbirth.