Down Syndrome

It’s become a controversial issue; should you screen for Down syndrome? And if the foetus shows signs of having a genetic abnormality, what should you do? Is abortion an option?
Many parents of Down syndrome children will say having a child with this condition is extremely difficult but incredibly rewarding.

What is Down syndrome?

Down syndrome is a genetic disorder that causes mental retardation and physical defects. It’s caused by the presence of an extra copy of chromosome number 21. Essentially what happens is at the time of conception; a baby inherits 23 chromosomes from its mother and 23 chromosomes from its father. In the case of a Down syndrome baby, the foetus inherits an extra chromosome. It’s this extra bit of genetic material that leads to Down syndrome.

This condition affects 1 in every 800 to 1000 live births. This is just a fraction of total cases, as early detection methods now allow parents to abort pregnancies when faced with a high risk of having a child with Down syndrome.

Who is more at risk?

It ’s not exactly known what causes Down syndrome. Scientists do however know that women older than 35 are significantly more at risk of having a child with this condition.

A woman who is 20 has a 1 in 1600 chance of conceiving a child with Down syndrome. That’s compared with a woman in her 40’s, who has a 1 in 100 chance and a woman older than 45 who has a 1 in 30 chance.

If you already have a child with this condition, you are more likely to have another Down syndrome child. For every 100 couples who have another baby, 1 will have a second child who has Down syndrome.

Because of these high statistics, most doctors now offer amniocentesis to women, usually older than 35. In some cases, younger women, with a family history of Down syndrome or other chromosomal abnormalities, can also opt to be tested.

The tests

There are two types of prenatal tests available to detect Down syndrome: screening tests and diagnostic tests. Screening tests estimate the risk that a foetus has the condition while a diagnostic test will tell whether the foetus actually has Down syndrome.

Screening tests include:

• Nuchal translucency testing uses an ultrasound to measure the thickness of the clear space in the tissue behind a foetus’s neck. Should the baby have Down syndrome, the Nuchal fold will be larger than normal. This test is correct 80 percent of the time, when considered along with the mother’s age. The Nuchal translucency test is done between 15 and 20 weeks of pregnancy.
• Blood tests will measure the amount of certain substances in the mother’s blood. This, along with the mother’s age, will determine whether more tests must be conducted. These tests are usually done between 11 and 20 weeks of pregnancy

Diagnostic tests include: 

• Amniocentesis involves removing a small amount of amniotic fluid, by inserting a needle into the mother’s abdomen. The cells are then analysed for the presence of abnormalities. Amniocentesis carries a small risk of complications, including preterm labour and miscarriage. This test is usually conducted in the 12th week of pregnancy.
• horionic-villus sampling (CVS) involves taking a sample of the placenta, also using a needle. In this case the doctors will also be looking for chromosomal abnormalities, but the test can be done earlier than an amniocentesis. This is usually performed at around 10 and half weeks of pregnancy. CVS also carries with it a small chance of miscarriage.

New guidelines now recommend that women of all ages be screened non-invasively for Down syndrome before the 20th week of pregnancy [John Hopkins Medicine]. Screening is a non-invasive procedure that doesn’t threaten the foetus. Researchers are investigating ways to locate and screen a few foetal cells that float through the mother’s blood stream.

If your test is positive for Down syndrome

If your doctor has conducted one or more of the tests and has concluded that your baby will have Down syndrome, you’re likely to feel completely overwhelmed. You may grieve for the problem free baby that you dreamed of having. Acknowledge what you’re feeling and once you’ve allowed yourself to process the news, investigate what it would mean to have a child with this condition.

Your doctor will be able to advise you on the best way forward. If the genetic abnormality is picked up early enough, you may decide to abort. However, talking to parents of children with Down syndrome, may give you a better perspective of what you can expect, once your baby is born.

Many children with Down syndrome grow up to lead completely normal lives. Some are able to go to school while others are able to hold down jobs, while still staying at home.

http://www.wolfson.qmul.ac.uk/epm/screening/diagnostic.html