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
|Can be done before,
during, or after
|Blood or saliva
sampling of mother
|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
*AFP- Quad Screen
|Free Fetal DNA
|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
|Blood sampling of
|Diagnostic Tests||Shows if the fetus has a
|Is performed during the
1stor 2nd trimester of
|Amniotic fluid or
samples from the
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: