Chromosomal abnormalities are structural or numerical abnormalities of chromosomes that typically occur as random errors in the division of sex cells. More specifically, egg cells (in the mother) and sperm cells (in the father) are affected.
The most common chromosomal abnormalities are numerical. They are referred to as trisomy chromosomal disorders. The most frequently occurring example of a trisomy disorder is Down syndrome or trisomy 21. Down syndrome is referred to as trisomy 21 because individuals diagnosed with this condition have three copies of the twenty-first chromosome. Other trisomy disorders include trisomy 13, trisomy 18, and trisomy 21. It is important to understand that any woman can have a child with a chromosomal disorder. However, there are certain risk factors that increase the risk of giving birth to a child with one of these conditions.
Advanced Maternal Age of 35 Years or Older
One major risk factor for trisomy disorders is being 35 years old or older during pregnancy. Some researchers believe this is because as women age, they are more likely to have errors occur during the sex cell division process, affecting the chromosomes in fertilized eggs.
Family History of a Chromosomal Abnormality
Most chromosomal abnormalities typically occur as a random error. However, there is a small percentage of cases that occurs due to inheriting a chromosome with a structural abnormality. Although this chromosome does not cause health complications for the parent, when passed on to the child, this abnormality can result in a chromosomal disorder.
Previously Giving Birth to a Child With a Chromosomal Abnormality
Giving birth to a child with a genetic disorder may increase the risk of chromosomal abnormalities with subsequent pregnancies. For example, couples who have previously had a child diagnosed with Down syndrome have a slightly increased risk of having another child with the condition. If you have a child that has been diagnosed with Down syndrome and would like to understand the risks associated with subsequent pregnancies, talk to a genetic counselor.
Abnormal Fetal Ultrasound Results
Chromosomal disorders are often associated with physical defects such as abnormalities of the spine, cleft palate, and heart defects. If your doctor notices any abnormalities in the development of your child during a routine ultrasound exam, he/she may recommend further testing to rule out or confirm a diagnosis of a chromosomal disorder.
Prenatal Testing Options for Women in a High-Risk Group
If you belong to one of the higher-risk groups mentioned above, your doctor may recommend prenatal testing. Noninvasive prenatal testing is a screening test that identifies the risk that a child will be born with a chromosomal abnormality. Noninvasive prenatal genetic screening can be performed as early as week 9 in pregnancy without the risks associated with diagnostic procedures, which are more invasive. If results show a high risk of a chromosomal abnormality, your doctor will present you with the option of diagnostic testing to obtain a definitive diagnosis.
Information collected from these tests can give couples time to prepare for the arrival of their child. An early diagnosis allows couples, with the help of their doctor, to organize any necessary medical care.
Want to Learn More About Chromosomal Abnormalities?
If you believe that you are at a higher risk of having a child with a chromosome abnormality and would like to learn more about the conditions associated with these anomalies, make an appointment with a genetic counselor. A genetic counselor is a specially trained healthcare provider who can educate couples about their risk of having a child with certain genetic disorders and explain relevant prenatal testing options. Additionally, you can find more information on chromosomal abnormalities on the National Human Genome Research Institute website.