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Testing for Down’s syndrome in Singapore

Down’s syndrome is a condition due to a defect in the baby’s chromosome. It is usually related to the age of the mother. The more elderly the pregnant mother is the higher the chances of delivering such baby. The baby usually has low mentality with a smaller head and sloping eyes (like those of Mongolian child). The nose is usually flat and the ears are set low. There may be abnormalities in the heart as well as intestinal problems. It can be diagnosed by Amniocentesis and Chorionic villus sampling.

Triple blood test

Triple blood test is a test of a set of 3 substances (alpha-fetoprotein, HCG and Oestriol) in the blood of the pregnant mother. It is usually done around the early stage of second trimester (about 14 to 18 weeks of pregnancy). It is a screening and not a diagnostic test. In other words, a positive result does not mean that the baby definitely has Down’s syndrome; rather that further test such as amniocentesis is necessary to reach a conclusive diagnosis. A negative test does not mean that the baby is perfectly healthy.

Amniocentesis

Amniocentesis is an invasive diagnostic test to detect abnormal chromosomes in the baby. The most common chromosomal abnormality is Down’s syndrome. It involves withdrawing liquid that surrounds the baby (Amniotic fluid). It is usually done at about 16-19 weeks of pregnancy. The skin of the abdomen is cleaned and numbed with a local anesthetic. Under ultrasound guidance, a long thin needle is passed into the womb and about 20 cc of amniotic fluid is obtained. Fetal cells that float in the amniotic fluid can then be cultured. Any abnormal chromosomes can then be identified. The result usually takes 2 weeks for all the 23 pairs of chromosomes to be analyzed. The risk of amniocentesis is miscarriage being 1/2 to 1%. Other risks include injuries to the baby, placenta, umbilical cord; infection of the womb and premature birth.

Chorionic Villus Sampling (CVS)

Like amniocentesis, CVS is an invasive diagnostic test to detect genetic abnormalities of the baby. It is done at about 9-11 weeks of pregnancy using a sharp instrument to obtain a small piece of placental tissues through the birth canal. The tissue is then cultured to provide analysis of the chromosomes. The advantage is that the test is done at an earlier period of pregnancy, so that the mother can know the results earlier. However, the risk of miscarriage is higher than that of amniocentesis and placental cells may have different chromosomes from those of the developing baby.

Source: Dr. Peter Chew

Dr. Chew is a consultant obstetrician and gynaecologist at Gleneagles Hospital. He is also a founding member of aLife, a voluntary welfare organization dedicated to nurturing a healthy respect for fertility and family life. For more information, visit www.alife.org.sg

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