Chromosomal Testing
What are chromosomes?
Genes are tiny groupings of hereditary material that make up your DNA. DNA is a ‘road map’ of what personal features or characteristics people have and can be found in chromosomes. Each cell in your body has 23 pairs of chromosomes for a total of 46.
Each egg and sperm have a total of 23 chromosomes, which make up a baby’s 46 total chromosomes.
Females have an (XX) chromosome and males have (XY).
What are birth defects?
A birth defect is an anatomical or functional abnormality that can cause mental and physical disabilities. Birth defects occur in approximately 3-5% of all pregnancies. They can be caused by genetic, chromosomal or environmental causes.
There are several different types of birth defects, the most common are:
- Aneuploidy – missing or extra chromosomes
- Trisomy 13, 18, or 21 (extra chromosomes)
- Monosomy or Turner’s Syndrome (missing chromosome)
- Microdeletions – only part of a chromosome is missing
- Spinal Muscular Atrophy
- DiGeorge Syndrome
- Inherited Disorder – genetic disorders passed down through families
- Sickle Cell disease (African-American)
- Tay-Sachs (Ashkenazi Jewish)
- Cystic Fibrosis (non-Hispanic white)
- Fragile X
- Environmental – Chemicals, medications, smoking, alcohol, other harmful agents
There are different types of genetic tests:
| Type of Test | What’s it for? | When can it be done? | How is it done? | Which test? |
|---|---|---|---|---|
| Carrier Tests | Shows if mother or father are carrying a gene for an inherited disorder. |
Can be done before, during, or after pregnancy |
Blood or saliva sampling of mother and/or father |
*Counsyl *HerediT |
| Screening Tests | Shows if the fetus has a potential for having a disorder. It is NOT a definite ‘yes or no’ test. |
Should be performed during 1st or 2nd trimester of pregnancy |
Blood sampling of mother and/or by ultrasound |
*Nuchal Translucency or *AFP- Quad Screen |
| Free Fetal DNA Screening Tests |
Fetus’ DNA, which has crossed into the mother’s blood stream via the placenta, can show chromosomal dis- orders- 98% accurate. |
Can be performed during the first trimester of pregnancy |
Blood sampling of mother |
*Harmony *MaterniT *Panorama *Verify |
| Diagnostic Tests | Shows if the fetus has a genetic condition. |
Is performed during the 1stor 2nd trimester of pregnancy |
Amniotic fluid or samples from the placenta are collected. |
*Amniocentesis *Chorionic Villi Sampling |
Should you be tested?
Although many babies born with birth defects are born to couples without risk factors, you may want to consider these factors:
- You or the baby’s father has a genetic disorder.
- You have a child with a genetic disorder.
- There is a family history of a genetic disorder.
- You belong to an ethnic group that has a high rate of a genetic disorder.
- You will be 35 or older at the time of delivery.
- You have abnormal screening test results.
Why should you be tested?
It is your choice as to whether or not to have genetic testing done. Knowing whether your baby is at risk of or has a birth defect beforehand allows you to prepare for having a child with a particular disorder. It will give you time to speak to a genetic counselor, learn about the specialized needs your baby may have, organize the appropriate medical care your baby may need, and maybe even find a local support group. You also may choose not to continue the pregnancy.
What do I do next?
Talk to your provider and together you can discuss which test(s) best suit your individual concerns based on your personal risk factors. If you would like more information, please visit:
