Prenatal Genetic Screening and Testing

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PrenatalMost babies are born healthy, however many parents-to-be are still worried that something could go wrong before the birth of their child.

WHO IS AT A HIGHER RISK FOR HAVING A CHILD AFFECTED WITH A GENETIC DISORDER?


• A woman age 37 or greater.
• A couple who already has a child with a genetic disorder.
• A couple with a family history of a genetic disorder.

There are two types of tests that can be done during pregnancy.

These include

Screening Tests – these tests cannot give you definitive information about the fetus, but can tell if you are at an increased risk of having a baby with birth defects.

Diagnostic tests – are offered if any of the screening tests show a high risk for fetal abnormality. Chorionic Villus Sampling and Amniocentesis test the fetus’s genetic material and therefore can tell you definitively if the baby is affected with a genetic disorder or not. As these are invasive tests, there is a risk of miscarriage associated with the procedures.

Non-Invasive prenatal testing (NIPT)

A simple test using the mother’s blood can now tell doctors more about the pregnancy than ever before. Did you know that pieces of the baby’s DNA circulate in the maternal bloodstream?

DNA is the blueprint of life—it holds all of the genetic information required for our bodies to function. DNA carries this genetic information on chromosomes. Healthy humans have 23 pairs of chromosomes. Any more or less can lead to problems.

NIPT is a screening test that analyzes the fetal DNA (cell-free or cfDNA) that circulates in the maternal blood to determine the baby’s risk for a number of genetic abnormalities.

What conditions can the test detect?

The test screens for the most common chromosomal abnormalities, which can cause serious birth defects, intellectual disability, or other problems in the baby. The test can also tell you the sex of your baby, if you wish to know.

The test can also detect abnormalities of the sex chromosomes:

Turner syndrome (Monosomy X), which is caused by a missing X chromosome in females. The disorder may cause heart defects, hearing problems, stunted growth, infertility and minor learning disabilities. Many pregnancies with Turner syndrome miscarry before delivery.

Klinefelter syndrome (XXY), which is caused by an extra X chromosome in males. The disorder may cause delayed or absent puberty, learning difficulties and tall stature. Most males with Klinefelter syndrome are infertile.

XYY or XXX syndrome, which is caused by an extra Y chromosome in males or an extra X chromosome in females. Individuals with this disorder may have tall stature and an increased risk for learning difficulties or delayed motor skills. Fertility is not usually affected and some individuals have no symptoms at all.

If your healthcare provider recommends it, the test can also screen for the following conditions, which are not routinely tested:

Trisomy 9, an extra copy of chromosome 9 Trisomy 16, an extra copy of chromosome 16 Common micro-deletions such as DiGeorge syndrome, Angelman syndrome, Prader- Willi syndrome, Wolf- Hirschhorn syndrome and Cridu- chat syndrome— which are all caused by the loss of a small piece of a chromosome.

What will the Results Represent?

If your results are normal, this means that the disorders tested for were not detected, which can provide significant reassurance. In the case of an abnormal result, your healthcare provider will discuss what that means for your pregnancy and will offer a diagnostic test such as CVS or
Amniocentesis to confirm the result.

When Can the Test be Done?

The test can be performed from week 10 onwards of the pregnancy.

A Non-invasive Prenatal Test Can Screen For

Down syndrome (Trisomy 21), which is caused by an extra copy of chromosome 21. The disorder is the most common genetic cause of intellectual disability, and it may also cause heart defects, other organ defects, and hearing or vision problems. Edwards syndrome (Trisomy 18), caused by an extra copy of chromosome 18. The disorder causes severe intellectual disability along with serious defects of the heart, brain and other organs. Babies with Edwards syndrome usually survive less than one year. Patau syndrome (Trisomy 13), caused by an extra copy of chromosome 13. The disorder causes severe intellectual disability and many serious birth defects. Babies with Patau syndrome usually survive less than one year.

CREDIT:

(Written by Sonika Sachanandani-Phulwani-Genetic Counselor)
Contact: Sachanandani.sonika@gmail.com

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