Array CGH is an accurate genetic technique for prenatal diagnosis of very small changes in genetic material that are not detected by karyotyping. These changes can be: microdeletions (absence of a very small piece of chromosome) and microduplications (addition of a piece of chromosome). Both defects can cause diseases that affect the intellectual and physical development of carriers. It does not identify point mutations or chromosomal alterations in equilibrium (balanced translocations). An array CGH requires an amniocentesis or chorionic villus sampling to obtain the necessary sample (amniotic fluid or chorionic villi, respectively). An array CGH is especially recommended if: Abnormal findings are observed on ultrasound: organ malformation in combination with growth retardation or multiple malformations. If there are abnormal chromosomal findings that need to be further clarified. If the prospective parents have a great need for reassurance and want very detailed information about the chromosomal picture of the foetus.