By Dr Lynda Nazareth

Down’s syndrome is one of the most common chromosomal abnormalities that affects approximately 1 in 1,000 to 1 in 1,100 live births worldwide, according to the World Health Organization. It presents a spectrum of physical, developmental, cognitive and medical challenges. India is home to 61,000 children born with this genetic disorder every year. 

Down’s syndrome, also spelled as Down syndrome and known as Trisomy 21, occurs when an individual possesses an extra copy (partial or full) of chromosome 21. This extra genetic material is responsible for the clinical presentation.

However, how the extra chromosome appears is still unknown. Late pregnancies pose a high risk for a baby with Down’s syndrome, some statistics state.

Down Syndrome exists in three different types. In about 95% of cases, it happens due to a cell division error called nondisjunction. A rare form called mosaicism causes around 2% of cases, while another type, translocation, accounts for about 3%.

5 Facts About Down’s Syndrome

• About one-third (33%) of translocation cases of Down syndrome are inherited, which means they make up around 1% of all Down syndrome cases.


• If the father carries the translocation gene, there’s a 3% chance the baby will have Down syndrome.


• If the mother is the carrier, the risk of having another child with Down syndrome rises to 10-15%.


• Advancements in diagnostics and prenatal screening allows the screening for Down syndrome as early as 10 weeks of gestation.


• Prenatal testing is the most effective method to predict the possible problems that could affect the baby. It gives you a risk or a probability that a particular condition exists. 

According to the American College of Obstetricians and Gynaecologist (ACOG), all pregnant women should be offered an option of screening or diagnostic testing for foetal genetic disorders regardless of maternal age.

Down Syndrome Screening Methods

Prenatal screening can be done by two methods: Biochemical screening and non-invasive prenatal testing. Biochemical screening includes dual marker screening, quadruple marker screening, which is based on the mother’s hormones, and ultrasound findings (Nuchal translucency, crown rump length, soft tissue markers). Biochemical screening markers can detect about 85-90% of Down syndrome cases.

Non-invasive prenatal testing, or NIPT, or cell-free DNA analyses the foetal DNA fragments present in the mother’s blood to determine whether the baby is at an increased risk of Down's syndrome. The detection rate of NIPT is as high as 99% and a false positive rate of less than 1%. 

Why Screening Tests For Down's Syndrome

The purpose of a screening test is only to identify a subset from the screened population to whom the diagnostic test (e.g., chorionic villus sampling/amniocentesis) needs to be offered. A positive screening test does not necessarily mean the baby has Down syndrome— it only indicates a higher risk and should be followed by diagnostic testing.

The receipt of the results of early Down syndrome screening can be an emotional turmoil irrespective of the outcome. It is extremely important to connect with the right people and not panic. Gynaecologist, feto-maternal medicine expert or geneticist could help with understanding of the results, genetic counselling and helping in decision making as to what needs to be done next. Early testing helps in early diagnosis, early intervention and care. Early intervention is an important component in managing Downs syndrome.  

Dr. Lynda Nazareth, Consultant Pathologist, Metropolis Healthcare Limited.

[Disclaimer: The information provided in the article, including treatment suggestions shared by doctors, is intended for general informational purposes only. It is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified healthcare provider with any questions you may have regarding a medical condition.]