Prenatal Screening for Chromosome Disorders
Prenatal screening for chromosome disorders by maternal serum screening, ultrasound and non-invasive prenatal tests, such as Harmony®, is an established part of reproductive care in Australia.
The overall risk of chromosome disorders rises markedly with maternal age, as shown in Figure 1. (There are two exceptions: Monosomy X, also known as Turner syndrome, and microdeletions, such as 22q11.2, occur independently of maternal age). This does not mean that chromosome screening should be restricted to older mothers.
Younger mothers have more babies than older mothers, and the overall outcome is that the majority of pregnancies with a serious chromosome disorder occur in mothers under 35 years of age. For this reason, screening for chromosome disorders in pregnancy should be offered to mothers of all ages.
The great majority of these chromosome disorders are new abnormalities that have happened for the first time in this pregnancy. They are not inherited disorders, and genetic testing of the parents provides no information about the risk of such an abnormality. This provides another reason for offering screening for chromosome disorders to all mothers, irrespective of family history.