Detecting Down syndrome in second trimester of pregnancy?

(February 23, 2010)

Down syndrome or Trisomy 21 is caused when an extra gene causes delay in the development of your child. Your child may suffer from some physical and mental developmental problems. This condition cannot be prevented; however, it can definitely be detected well in advance, before the baby is even born.

Normally, at the time of conception, a baby inherits 46 chromosomes from the parents, 23 from the mother and 23 from the father. In some cases, a baby may receive an extra chromosome, making the total 47 instead of 46. This extra genetic material causes physical developmental issues and also delays the mental development in children, leading to Down syndrome.

There is no proper explanation till now as to why and how a baby can inherit the extra chromosome, and there is no way to prevent this condition either. It has been noticed that babies of women who conceive after the age of 35 are more prone to this condition. There are two types of prenatal tests that are conducted in order to detect this condition.

Screening tests. Screening tests help to estimate the risk that a fetus will have Down syndrome. Screening tests are easy to perform and are cost-effective too. They help the parents in deciding whether they need to go for further diagnostic tests.

There are four types of screening tests, as mentioned below.

•    Nuchal translucency testing: This test is done between 11 to 14 weeks of pregnancy. This method uses an ultrasound to measure the clear space between the folds of tissue behind the baby’s neck. This measurement, long with the mother’s age and baby’s gestational age, helps in calculating if the baby has this condition. It is done along with the mother’s blood test.

•    Quadruple screen: Also known as the multiple marker test, it helps in measuring the quantities of normal substances in your blood. This is done between 15 to 18 weeks of pregnancy.

•    Integrated screen: This type of screening uses the results from the first and second trimester screening tests to arrive at the most accurate result.

•    Genetic ultrasound: A detailed ultrasound performed around 18 to 20 weeks, along with a blood test, helps in checking the physical traits of the baby and also for abnormalities, if any.

Diagnostic tests. The second type of test is called a diagnostic test. With the help of a diagnostic test, it becomes easier to detect if the baby has already got Down syndrome.

Diagnostic tests are more accurate as they are performed inside the uterus. They help in detecting the risk of a possible miscarriage and other complications associated with this condition. There are three types of diagnostic tests.

•    Chorionic villus sampling: A tiny sample of the placenta, taken either through cervix or with the help of a needle inserted through the abdomen, is tested to check for Down syndrome. This test is done in the first trimester, and it carries a slightly higher risk of a miscarriage as compared to other methods.

•    Amniocentesis: This test is done between 18 to 20 weeks of pregnancy. A small amount of amniotic fluid is removed with the help of a needle. The cells are then analyzed for chromosomal defects. This can cause preterm labor or a miscarriage.

•    Percutaneous umbilical blood sampling: Performed around 20 weeks of pregnancy, in this test, a small amount of blood is removed from the umbilical cord using a needle. Again, this test can cause preterm labor or a miscarriage

Submitted by P T on February 23, 2010 at 10:57

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