Test that accurately detects down syndrome in a baby as early as within 3 months of pregnancy


Lord of Penmai
Jul 5, 2011
Test that accurately detects down syndrome in a baby as early as within 3 months of pregnancy

A simple blood test can now accurately tell a pregnant mother, as early as three months into her pregnancy, whether her child suffers from Down's syndrome.

Researchers on Friday announced the first ever non-invasive first trimester blood test to reliably detect the syndrome that affects thousands of children annually.

The routine screening uses a non-invasive test that analyzes fetal DNA in a pregnant woman's blood.

It can accurately detect Down's syndrome and other genetic fetal abnormalities in the first trimester.

Every year between 23,000 and 29,000 children are born in India with Down Syndrome, which is the highest in the world.

Current screening for the syndrome or trisomy 21 includes a combined test done between the 11th and 13th weeks of pregnancy, which involves an ultrasound screen and a hormonal analysis of the pregnant woman's blood.

The results suggest that the test is superior to currently available screening strategies and could reshape standards in prenatal testing.

Researchers from King's college London carried out the new test on 1005 pregnancies at 10 weeks and found a lower false positive rate and higher sensitivity for fetal trisomy than the combined test done at 12 weeks.

Two other tests - chorionic villus sampling and amniocentesis can definitely detect or rule out fetal genetic abnormalities.

But these are invasive to the pregnancy and carry a high risk of ending up in miscarriage.

Several studies have shown that non-invasive prenatal diagnosis for trisomy syndromes using fetal cell free (cf) DNA from a pregnant woman's blood is highly sensitive and specific, making it a potentially reliable alternative that can be done earlier in pregnancy.

The study by Kypros Nicolaides from King's College London is the first to prospectively demonstrate the feasibility of routine screening for trisomies 21, 18, and 13 by cfDNA testing.

In the new test, both cfDNA and combined testing detected all trisomies but the estimated false-positive rates were 0.1% and 3.4%, respectively.

The authors said, "This study has shown that the main advantage of cfDNA testing, compared with the combined test, is the substantial reduction in false positive rate. Another major advantage of cfDNA testing is the reporting of results as very high or very low risk, which makes it easier for parents to decide in favor of or against invasive testing."

A second study by the same group, which included pregnancies undergoing screening at three UK hospitals between March 2006 and May 2012, found that effective first-trimester screening for Down's syndrome could be achieved by cfDNA testing contingent on the results of the combined test done at 11 to 13 weeks.

The strategy detected 98% of cases, and invasive testing was needed for confirmation in less than 0.5% of cases.

"Screening for trisomy 21 by cfDNA testing contingent on the results of an expanded combined test would retain the advantages of the current method of screening, but with a simultaneous major increase in detection rate and decrease in the rate of invasive testing," the authors concluded.

Down's Syndrome Foundation of India says chromosomes are thread-like structures composed of DNA and other proteins. They are present in every cell of the body and carry the genetic information needed for that cell to develop. Human cells normally have 46 chromosomes that can be arranged in 23 pairs. Of these 23, 22 are alike in males and females; these are called the "autosomes".

The 23rd pair is the sex chromosome.

Human cells divide in two ways. The first is ordinary cell division by which the body grows. In this method, one cell becomes two cells that have the exact same number and type of chromosomes as the parent cell. The second method of cell division occurs in the ovaries and testicles and consists of one cell splitting into two, with the resulting cells having half the number of chromosomes of the parent cell. So, normal eggs and sperm cells only have 23 chromosomes instead of 46.

The test in which blood or skin samples are checked for the number and type of chromosomes is called a karyotype. The most common cause of Down syndrome occurs when an infant is born with three, rather than two, copies of the 21st chromosome (known medically as trisomy 21).

Some investigators reported that older fathers might also be at an increased risk of having a child with Down syndrome.
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