Down’s Syndrome

Screening for Down’s Syndrome

What is Down’s Syndrome?

Down’s syndrome is a genetic condition (that is a condition the affected person is born with) . It is caused by the presence of an extra chromosome (chromosome number 21). The affected person has 3 of this chromosome instead of a pair as in normal individuals. Hence, the medical name for this condition is Trisomy 21.

What causes Down’s Syndrome ?

Inside the cells which make up the human body are tiny structures called chromosomes which carry our genes. Most people have 23 pairs of chromosomes in each of their cells. When the body produces special cells needed to make babies, the chromosome pairs divide and rearrange themselves.

Sometimes by accident, chromosome number 21 fails to divide, and the baby’s cells have an extra chromosome no 21. This accident is not due to anything the parents have or have not done. This extra chromosome cannot be removed from the Baby’s cells.

Incidence:

The overall incidence of Down’s syndrome is 1 in 700 live births. It usually does not run in families. Anyone can have a baby with Down’s syndrome, but, the risk does increase with the age of the mother. At age 20, the chance of having a baby with Down’s syndrome is 1 in 1500(0.07%). At age 30, it is 1 in 900 (0.1%). At age 40, it is 1 in 100 (1%). At age 45, it is 1 in 28 ( 3.57%).

Physical Characteristics of Down’s Syndrome:

Skin deficient in elasticity, giving the appearance of being too large for the body. Flat face with a small nose.

Other features:

Learning difficulties, some more serious than others.  Most people with Down’s syndrome require long term help and support.  Life expectancy is between 50 and 70 years.

Health problems:

Heart problems

Reduced hearing and vision.

Alzheimer’s disease may affect people with Down’s syndrome earlier than others.

But, people vary ,and, some people with Down’s syndrome enjoy good health.

Screening for Risk of Down’s Syndrome in the first trimester

This is not a diagnostic test.

This screening test is non- invasive and consists of the following:

1. A special ultrasound scan of the baby between the ages of 11 weeks and 13 weeks 6 days, measuring the amount of fluid lying under the skin at the back of the baby’s neck( Nuchal translucency scan). At Insight Medical Ultrasound, this special ultrasound scan is done only by experienced sonographers who are certified by the Fetal Medicine Foundation.

   
   

2. Blood test : A sample of the mother’s blood , usually taken immediately after the special ultrasound scan. The sample is sent to a laboratory accredited by the Fetal Medicine Foundation which measures the serum extracted from the mother’s blood sample for two biochemicals: free beta HCG ( human chorionic gonadotrophin) and PAPP-A (pregnancy associated plasma protein).Our partner laboratory is CPA (Clinical Pathology Accreditation) accredited and Fetal Medicine Foundation certified service. The laboratory takes part in the 6 monthly review of services by DQASS (Down‘s Syndrome Quality Assurance Support Service).

    

3. The results of the special ultrasound scan and blood tests are analysed by a computer using sophisticated software developed by the Fetal Medicine Foundation. The result is expressed as a Risk of the baby having Down’s syndrome. If the risk of the baby having Down’s syndrome is greater than 1 in 250, the mother is  referred to her midwife/ doctor to discuss the results who will give more information and support. Usually, the mother is offered a diagnostic test.

    

    

    

    

          This test has a detection rate of 85-90%.  

This test is as per current NICE (National Institute of Clinical Excellence) guidelines.