CHENNAI: With one in 800 children having chromosomal abnormality causing Down syndrome, the condition can be diagnosed at a very early stage of pregnancy, thanks to the recent advancement in medical technologies. Based on the diagnosis, expectant parents can plan for the future course of action, say medical experts.
Down syndrome is a genetic chromosomal abnormality that are some are born with. Each cell in the human embryo should contain 46 chromosomes or 23 pairs of chromosomes, equally contributed by the mother and the father. That is 23 from the mother and father each. But some children will carry 47 chromosomes due to the presence of multiple copies of chromosome number 21.
The initial diagnosis is often based on the baby’s appearance, but there are chances the features associated with this genetic disorder can also be found in babies without Down syndrome. “But the chromosomal Karyotype test using blood sample would help to suspect the condition,” says Dr Kavya Krishnakumar, consultant obstetrician and gynaecologist at Motherhood, Chennai.
The risk of having a baby with Down syndrome increases in cases where the pregnant woman is 35 years or older. “Also in cases where the woman has had a child with Down syndrome in the past. So, the test is recommended for this kind of suspected cases,” explains Dr Kavya.
Ultrasound and blood tests are advisable. Screening tests can be done either in the first trimester or the second trimester of pregnancy. Blood is tested for abnormalities in the value of two particular proteins — human chorionic gonadotropin (HCG) and pregnancy associated plasma protein (PAPP-A).
NT scan (Nuchal Translucency) is recommended. This scan measures the baby’s neck to see if abnormalities are present; it will also check for nasal bone deformities.
During the second trimester, screening to measure the values of three proteins — alphefeto, estriol and HCG in the maternal blood, should be done. Also quadruple screening is done to measure one more additional protein ‘inhibin A’ in the maternal blood. There is a recently-launched screening method called cell-free fetal DNA analysis, which will check the fetal DNA circulating in the mother’s blood.
However, these basic screening tests are not foolproof. These will only indicate whether the baby has a higher probability of having Down syndrome. For 100% confirmation of the disorder, tests like amniocentesis and chorionic villous sampling are being done.
“But these tests are invasive and there is risk of miscarriage. That’s why they must be done only with a doctor’s recommendation,” adds Dr Kavya.