How Is Your Blood Screened for Babys Chromosomes

Testing for Down syndrome and other chromosome abnormalities

Information for expectant parents

What are chromosome abnormalities?

Chromosomes carry our private genetic material (genes). Our bodies are made upwardly of billions of cells, and in each prison cell in that location are 23 pairs of chromosomes. Extra or missing chromosomes may cause abnormalities that can affect a baby'south development. The most common chromosome aberration affecting newborns is Downwardly syndrome which occurs in around 1 in 500 to 600 pregnancies.

Down's syndrome (trisomy 21)

Down's syndrome (as well known as trisomy 21) is a genetic condition—it is non an illness or a affliction. Down syndrome is caused by the occurrence of an extra chromosome; chromosome 21. This results in a range of physical features, wellness issues, developmental delay and some level of intellectual disability. In most cases there is no family history of Downwards syndrome every bit it ordinarily occurs randomly. Other chromosome abnormalities such as Edward syndrome (trisomy 18) and Patau syndrome (trisomy 13) occur less often than Down syndrome but have more than severe effects on the baby. Chromosome abnormalities cannot be reversed once they occur.

What tests are available?

• Screening examination—looks for signs that a baby may be at an increased run a risk of having a chromosome aberration, such as Down's syndrome. A screening test cannot determine that a baby definitely has a sure abnormality. Screening tests exercise not bear any risk to the female parent or babe.
• Diagnostic exam—can ostend whether or not the babe is affected past certain chromosomal abnormalities. Diagnostic tests carry a small gamble of pregnancy loss.

Screening tests

The Start Trimester Combined Screen (FTCS)

The FTCS involves an ultrasound scan of the infant at 11 to 13 weeks gestation (nuchal translucency scan) and a blood examination from the female parent at 10 to 13 weeks gestation (Papp-A and BHcg). The test combines the mother's age (the historic period of the egg if using a donor egg), weight, ethnicity, smoking status, claret exam results and ultrasound findings to point a level of risk for Down syndrome (trisomy 21), Edward syndrome (trisomy xviii) and Patau syndrome (trisomy 13). Other markers such as the nasal bone may be included in the assessment.

The level of risk is described every bit a number e.g. 1 in 100 which is the same as a one per cent gamble. A event is deemed loftier risk when it is more than 1 in 300 and low risk when less than 1 in 300.

Around five per cent of meaning women (i in 20) who have the FTCS will exist given a 'high run a risk' result but the majority of them will non be carrying a baby with a chromosome abnormality. Within this 'high risk' group will be well-nigh cases of Downward syndrome, Edward syndrome and Patau syndrome.

Effectually 95 per cent of pregnant women (19 in 20) who accept the FTCS will be given a 'low risk' result. Inside this 'low chance' group there will even so be some cases of Down's syndrome, Edward syndrome and Patau syndrome.

An ultrasound scan image showing the area at the back of the neck called the 'nuchal translucency'

The triple test or second trimester maternal serum screen

The triple examination is a blood test performed in the 2nd trimester of pregnancy at fifteen to 20 weeks gestation. It measures the levels of certain hormones in the female parent'southward blood to assess the risk of Downwardly syndrome, Edward syndrome, Patau syndrome and too neural tube defects (e.g. spina bifida). Dating the pregnancy by ultrasound is recommended for the triple test.

Around five per cent of pregnant women (i in 20) who have the triple examination will be given a 'high risk' event but the majority of them volition not be carrying a baby with a chromosome aberration. Within this 'high risk' group will be most cases of Downwards syndrome.

Around 95 per cent of pregnant women (nineteen in 20) who have the triple test will be given a 'low risk' result. Within this 'low risk' group there volition yet be some cases of Down's syndrome.

If the hazard for a neural tube defect (spina bifida) is 'high', an ultrasound scan is recommended every bit the diagnostic test.

Not-invasive prenatal testing (NIPT)

NIPT involves taking a sample of blood from the pregnant woman. This can be done from 10 weeks of pregnancy onwards. The blood sample is evaluated for the baby's Dna to make up one's mind a level of run a risk for Down syndrome (trisomy 21), Edward syndrome (trisomy 18) and Patau syndrome (trisomy 13).

It is important to empathize that NIPT is a screening and non a diagnostic exam. If the result comes back indicating a low risk for trisomies 21, xviii and 13, it is very unlikely (less than or equal to 0.1% take chances) that your infant has 1 of these disorders. If the result comes back indicating a high risk of trisomy, invasive testing with amniocentesis or chorionic villus sampling may be offered. Furthermore, this examination does non provide information about structural abnormalities. However, the benefit of the test is that information technology is not-invasive and not associated with an increased take chances of pregnancy loss.

NIPT is offered to loftier-risk women including those aged 35 years and over, those with an abnormal ultrasound, a personal or family unit history of aneuploidy, and an abnormal CFTS or triple test. Notwithstanding, NIPT can also be performed for low-gamble women.

This examination can exist performed for both singleton and twin pregnancies, although CFTS is the preferred test for twin pregnancies. For triplets and more, the nuchal translucency (NT) exam and measurement of the nasal bone is the preferred option.

The turnaround fourth dimension for NIPT results is upwards to 14 days. Upward to five per cent (ane in 20) of NIPT tests may non return a result due to insufficient quantity of fetal Dna in the maternal blood sample.

Diagnostic tests

Chorionic Villus Sampling (CVS) and amniocentesis are both diagnostic tests that can ostend whether or not a baby has a chromosome abnormality. They involve sampling of the placenta (CVS) or amniotic fluid (amniocentesis) and carry a adventure of pregnancy loss of between 0.5 and one per cent. For further information delight see Mater's brochure: Chorionic Villus Sampling (CVS) and Amniocentesis.

Oft asked questions

Should I accept more than one screening exam?

No. A screening test should just exist performed once. The aforementioned screening test should non be repeated. A triple test is not required if a FTCS has already been performed.

Are in that location whatsoever benefits to testing?

Informing the parents about potential issues during the pregnancy is a normal office of providing skillful antenatal care. Babies with chromosome abnormalities may require monitoring earlier birth for specific abnormalities eastward.g. cardiac malformations. In some circumstances, nativity may exist required in a specialised heart. Knowledge of a chromosome abnormality affecting the unborn baby may also influence when and how the babe is born. Data near health problems affecting their unborn baby gives parents the opportunity to seek further data, counselling and support.

Are in that location any downsides to testing?

Parents should consider the risks and benefits of all antenatal tests before proceeding. Testing for wellness problems affecting the unborn baby may create an unwelcome level of anxiety for some parents and relief for others. Diagnostic testing carries a small risk of pregnancy loss that has to exist weighed against the potential benefits of knowing early in pregnancy that a baby might take health problems. We encourage y'all to ask your wellness provider questions almost the possible risks and benefits of any suggested handling or tests, likewise as the range of possible outcomes.

What virtually the 18 to 20 week scan?

It is recommended that all women have an ultrasound in pregnancy between 18+0 to twenty+6 weeks to bank check for structural abnormalities, amniotic fluid volume and placental location. The 18 to 20 week scan is non recommended every bit a screening test for Down's syndrome due to its poor performance.

What if testing indicates a trouble?

Your wellness provider volition discuss the results of the tests with you lot. They can also arrange referral for further counselling or additional testing if required.

Can all abnormalities be ruled out?

The majority of babies are healthy at nativity. While some conditions such as Down's syndrome can exist tested for during pregnancy, not all abnormalities can exist ruled out. If you have concerns about any specific conditions e.thou. those that might be present in a family member, please hash out this with your wellness care provider.

How tin can I suit to have testing?

The first affair to do is to discuss available testing options with your wellness intendance provider. FTCS is performed in most local radiology practices accredited to perform the nuchal translucency browse. The nuchal translucency scan ordinarily incurs an out-of-pocket expense.

Mater Centre for Maternal Fetal Medicine (MFM)

Equally a tertiary referral centre MFM provides diagnostic testing by CVS or amniocentesis. Pre and post-process counselling is included as part of our service. Referrals for diagnostic testing by CVS or amniocentesis can exist faxed to 07 3163 1890. A referral from a doctor is required to access services provided by the heart. Bulk-billing is available for public patients referred from Queensland Health Hospitals and those holding Health Care cards. An estimate of fees can be obtained by contacting our reception staff on 07 3163 1896.

Contact details

Mater Center for Maternal Fetal Medicine
Level 7
Mater Mothers' Hospital
Raymond Terrace
South Brisbane Qld 4101
Phone: 07 3163 1896
Fax: 07 3163 1890
Website: www.matermothers.org.au

Further data and support

Genetic Wellness Queensland
Phone: 07 3636 1686
Website: http://www.health.qld.gov.au/ghq/default.asp

Downwards Syndrome Association of Qld
Phone: 07 3356 6655
Website: www.dsaq.org.au

Centre for Genetics Education
Website: www.genetics.edu.au

Fetal Medicine Foundation (Britain)
Website: www.fetalmedicine.com

Mater acknowledges consumer consultation in the development of this patient data.

Mater Doc Num: PI-CLN-430139

Concluding modified 18/10/2017.
Consumers were consulted in the development of this patient information.
Last consumer engagement appointment: 22/8/2017

For farther translated health information, you tin visit healthtranslations.vic.gov.au/ supported past the Victorian Department of Health and Human Services that offers a range of patient information in multiple languages.

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Source: http://brochures.mater.org.au/brochures/mater-mothers-hospital/testing-for-down-syndrome-and-other-chromosome-abn

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