Down syndrome
What is Down syndrome?
Chromosomes contain all our genetic material. The correct number and arrangement of chromosomes are necessary for the development of a normal individual.
Down syndrome is an abnormality of the chromosomes in which the individual has 3 copies of chromosome 21, rather than the normal 2 copies. For this reason, the condition is also called Trisomy 21.
Children with Down syndrome are born with a characteristic physical appearance that includes slanted eyes, a flat nose on a round head, and abnormalities on the palms of the hands and the soles of the feet. They often have multiple birth defects and a degree of intellectual impairment.
Down syndrome occurs in fewer than one in 870 births. Older women have a higher risk of having a baby with Down syndrome, but women of any age can give birth to a baby with Down syndrome.
Which tests screen for Down syndrome?
Pregnant women can choose to have antenatal screening tests that identify those at higher risk of having a baby with Down syndrome. These include blood tests and a specialised ultrasound, known as a nuchal translucency scan.
The nuchal translucency ultrasound is undertaken at 11 to 13 weeks of pregnancy, and measures the width of an area on the back of the neck of the fetus. Blood tests can be done to measure a protein called PAPP-A in the first trimester, and several hormone levels in the second trimester. These results can be combined to identify women at high risk.
High-risk women are then offered a confirmatory test. This test is invasive and involves either chorionic villous sampling (CVS) in the first trimester, or an amniocentesis in the second trimester. CVS involves removing some cells from the placenta, whereas amniocentesis involves testing the liquid that surrounds the fetus in the womb. These invasive tests carry a small risk of miscarriage (usually less than one per cent).
What health issues are associated with Down syndrome?
Down syndrome is often associated with several medical problems such as congenital heart disease, hearing loss, hypothyroidism (an under-active thyroid gland), cataracts and obstructive sleep apnoea. In addition, most children with Down syndrome will function in the lower range of intellectual abilities.
It is important that children with Down syndrome and their families receive support from their doctor, as well as other health professionals such as physiotherapists and speech therapists.
Last Reviewed: 16 May 2008
