Must-know facts about Down's syndrome antenatal screening
Created by Dr Himani Khanna Updated on Sep 30, 2018
You are pregnant and your gynaecologist has prescribed a screening test for Down’s syndrome. You cannot but think overtime about it: What is Down’s syndrome? How is the test done? Why do I need to undergo this test, when I am healthy and fine? So on and so forth! Our expert, Dr Himani Khanna, Developmental Paediatrician, Artemis, Gurgaon, answers the top concerns.
Q1. What is Down's syndrome?
In medical terms, Down's syndrome is a genetic chromosome problem. Children with Down’s syndrome have an extra copy of chromosome 21 in the cells of their body and this affects every part of their body. At conception, when the genetic bundles from the egg and the sperm fuse, they get this extra copy of chromosome 21 – also known as trisomy 21 (three copies of a chromosome).
In practical life, this manifests in learning difficulties, which can range from mild to severe and can also result in other serious health problems like congenital heart defects, congenital intestinal defects, hip and limb defects, blood cancer, among other medical complications.
Down’s syndrome can be diagnosed prenatally as well as postnatal. Test done to diagnose it prenatally include screening and diagnostic tests.
What you need to know:
- The screening tests are not confirmatory and carry no risk of miscarriage.
- The diagnostic tests are confirmatory and carry some risk of miscarriage.
Q2. Does the risk increase with an increase in the age of the mother?
Yes, the risk increases with the age of the mother and here’s a rough calculation of the risk:
- A 20-year-old woman has a 1 in 1,500 chance of having a baby with Down's syndrome.
- A 30-year-old woman has a 1 in 800
- A 35-year-old woman has a 1 in 270
- A 40-year-old woman has a 1 in 100
- A 45-year-old woman has a 1 in 50 risk or greater.
- About 1 in 100 women - with a previous Down's syndrome baby - will conceive another with this same ailment
Q3. Who should undergo Down’s syndrome screening and when?
All pregnant women should be recommended the Down’s syndrome screening between 10 and 20 weeks of pregnancy.
First screening at 11-13 wks of pregnancy
This screening includes an ultrasound (NTScan) followed by blood tests also called as Dual marker or dual screen is advised.
Second screen at 18-22wks of pregnancy
TIFFA (Targeted Imaging for Foetal Anomalies) which is an ultrasound, is done along with a Quadruple screen.
Q4. If the screening tests are positive, then what are the diagnostic/confirmatory tests?
In case the screening tests are positive, diagnostic tests are offered, which are confirmatory and in case the diagnostic tests are negative, no further testing is required.
The three main diagnostic tests that are used to diagnose Down's syndrome before birth are:
1. NIPT (Non-Invasive Prenatal Testing), which has a sensitivity of 99 percent.
2.Amniocentesis is a process of collecting amniotic fluid in the womb around the baby. This fluid contains cells shed from the baby’s skin, urine and waste products. These cells contain baby’s genetic material and are used to study the chromosome pattern of the baby. This test is done at 15 weeks (or later) of gestational age and has 1 percent risk of miscarriage.
3. Chorionic villus sampling (CVS) is where the genetic material is tested on the cells of the tissue, a sample of which is collected directly from the newly formed placenta. This test is conducted at 11 to 15 weeks of gestational age and has 1-2 percent risk of miscarriage.
In case, of family history or where one of the parents is already a Down’s syndrome patient, the diagnostic tests are recommended early, that is between 11-13 weeks of pregnancy.
Q5. In case the diagnostic tests are positive, what next?
In this case, the couple should immediately take an appointment with a Specialist Foetal Medicine Consultant, and also have detailed discussions with the gynaecologist and paediatrician so as to fully understand the implications of continuing or terminating the pregnancy and thereafter take an informed decision.
If the family and mother decide to continue the pregnancy, then the doctors may advise on the referral for an antenatal cardiac scan and any further scans or tests, and may also advise the couple on the choice of the place of delivery, which is well-equipped to deliver, receive and manage these babies after birth.
All said- Don’t judge children with Down’s syndrome based on their diagnosis because then you may miss out on their abilities, beauty and uniqueness. Have you or anyone you know undergone a Down’s syndrome screening? Please do share your experience as it will benefit other anxious mums out there. Look forward to your comments.
| Jul 25, 2017
My doctor asked my sister to take test for Down's Syndrome while she was pregnant, we were so scared of anything invasive. The Babyshield non-invasive prenatal test (NIPT) only helped. Today my nephew is healthy because we continued the pregnancy and becoz this test gave us 98% accurate result, without harming the baby nor mother.
| Jul 25, 2017
There is a comprehensive Prenatal testing platform called "BabyShield" powered by LifeCell. These guys cater every prenatal test available from a simple biochemical screening to Karyotyping. Get in touch with your doctor to know about BabyShield and get an accurate test result.
| Dec 20, 2016
thank you so much for sharing, I have under gone NT scan during my pregnancy, reports were all ok, but after delivery we got to know my baby suffering from congenital heart disease , he is having hole in his heart, really it's heartbreaking for me n my husband since we lost our first baby due to some other reason. we are consulting heart specialist from Narayana Hrudayalya, Bangalore , doctor said nothing to worry everything will be ok. now we are relaxed n my little prince doing well. God bless him with lots of love n health.