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3.09.2019
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Can Ultrasound pick up Down’s Syndrome?

One of the biggest concerns for expecting mothers is around the health of their baby. Fortunately there are a number of different scans and tests available to help predict the overall wellness of their baby. This is so they can prepare themselves for when the baby is born and if the baby will need any further medical attention after birth. On the contrary, if a pregnancy screens low risk for abnormalities, it puts the parents minds at ease knowing that their baby is healthy and safe.

 

What is Down Syndrome?

 

Down Syndrome occurs in 1 of 546 births in Ireland. Down Syndrome is diagnosed when a baby is born with an extra copy of chromosome 21. The exact cause of the extra chromosome that triggers this is still unknown. This extra gene is what changes the development of the brain and body. It can result in this person finding it harder to understand and learn new things. They may also struggle with everyday tasks and may experience social issues too. Babies who are affected by Down Syndrome often have distinctive facial features. Many Down Syndrome children can suffer from other health issues like heart conditions and hearing and vision problems too. Most of these can often be treated and shouldn’t be a major concern. For most people with Down Syndrome, they will live a good quality of life and go on to live until they are 60 plus. With the right support and care they can live semi-independently, get a job and have relationships.

 

Screening for Down Syndrome when you’re pregnant

 

First Trimester Screening

All women who are pregnant have a small risk of their baby being born with Down Syndrome, however maternal age is a factor when considering risk. The older the mother, the higher the chances are of having a baby with Down Syndrome. Using a combination of maternal age, presence or absence of major fetal abnormalities on ultrasound, Nuchal Translucency (NT) – fluid measurement behind the fetus’ neck, and the level of two proteins in their blood (Free-ß-hCG and PAPP-A), we can calculate the chances of the pregnancy being affected by T21 or T18/T13. The best time to perform this test is between 10 – 14 weeks into pregnancy. The model that we use at The Ultrasound Suite (along with the Bray Women’s Health Centre) is by taking a maternal blood specimen at 10 weeks and an ultrasound scan (which is usually done at 12 weeks). The biochemistry results can then be made available at the time of the NT scan and the combined test result can be calculated at the time of the appointment. This test will pick up 94% of cases affected by Down Syndrome.

 

Non Invasive Prenatal Testing (Nipt) 

This form of testing analyses cell-free fetal DNA that is present in the mother’s blood. It’s a new form of screening for Down Syndrome but also other conditions such as Edwards syndrome and Patau syndrome too. It can also test for X and Y chromosome conditions. This blood test can be performed from 9 weeks onwards and must be performed in conjunction with a dating ultrasound. NIPT has the highest accuracy rate for assessing fetal trisomy risk and can identify more than 99% of fetuses with Trisomy 21.

 

Detailed Anomaly Scan

A Detailed Anomaly Scan usually takes place around 19 – 23 weeks into the pregnancy. It creates a 2 dimensional black and white image that checks for major physical anomalies in the baby. This scan is probably the most important scan that takes place during a pregnancy as the fetus is the perfect size for all the organs to be assessed to see whether the baby has an obvious defect such as spina bifida or a cleft palate. There are many ultrasound features that can be identified to detect if Down Syndrome is present. Please note that the anomaly scan cannot detect all abnormalities and syndromes. Only 50% of Down Syndrome fetuses can be detected at the Detailed Anomaly Scan.

 

Diagnostic Testing

Amniocentesis or Chorionic Villus Sampling (CVS) are procedures performed by specially trained health professionals – usually Fetal Medicine Specialists. A CVS is normally performed between 11-13 weeks. It involves taking a small sample from the placenta for testing. Amniocentesis is performed after 15 weeks, whereby a sample of amniotic fluid is taken for testing, also using a needle. Both of these tests are done under continuous ultrasound guidance. They should not be offered to women who are at age-related risk alone. Due to the invasive manner of this testing, it is estimated that 1 in 100 women who undergo amniocentesis or CVS will miscarry. They should only be offered to women where there is a history of Down Syndrome, a previous pregnancy with a chromosomal abnormality or if any of the above mentioned ultrasound tests show a high risk for an anomaly.

 

Conclusion

Ultrasound scans aren’t a full-proof way of testing for Down syndrome in babies. They can detect some indications of potential markers that are commonly seen in Down Syndrome babies but can’t give a definitive answer. A Detailed Anomaly Scan done at 20 weeks can only detect 50% of Down Syndrome cases. First Trimester Screening, using bloods and Nuchal Translucency measurement, done between 10-14 weeks, can detect 94% of cases and Non-invasive Prenatal Testing (NIPT) from 9 weeks can detect 99% of Down Syndrome cases.

 

Only invasive tests (Amniocentesis and Chorionic Villus Sampling) can clinically confirm the presence of Down Syndrome in a baby. It’s important to note that up to 1 in every 100 women who receive invasive testing will miscarry. So it’s important to think it through before undergoing this form of testing.

Ultrasound Scan

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