What is genetic testing and why is it important to me and the welfare of my unborn child?
Genetic testing are tests which are performed during pregnancy to determine if any birth defects, syndromes, or chromosomal disorders may be present within the unborn fetus. There are several optional tests that are offered during pregnancy. These tests can provide information about a woman’s risk of having a baby with certain birth defects, so that making informed decisions and communicating about your concerns with your doctor – and family – can occur.
Are there any optional tests I should consider?
Testing may be right for some and not right for others, based on many factors. These factors include one’s risk of having an affected baby, one’s personal plans and needs, and one’s personal spiritual and religious beliefs.
We will discuss specific tests with you during your prenatal visits, but the decision to be tested or not is a personal decision between you and your partner. Many couples choose not to be tested for birth defects, and of course, we always honor the personal decisions of our patients in this regard.
In addition to the tests discussed below, there may be additional elective tests that we discuss with you based on your personal and medical history, family history, or ethnic background. The following discussion is not meant to be comprehensive, but is an overview of some of the standard elective tests offered to all pregnant women with our practice:
Chromosomal disorders may be caused by a missing, damaged, or extra chromosomes. In normal human development, there are 23 pairs of chromosomes, allowing for a total of 46 chromosomes. Sometimes, during the early stages of fetal development, something goes awry during cell division. This usually occurs during the cell division and replication phase known as “mitosis”:
mitosis – part of the reproductive cell cycle process by which chromosomes in a cell nucleus are separated into two identical sets of chromosomes, each in its own nucleus.
Most children with chromosomal disorders will have physical defects, and some have also incur mental defects. Two examples of more common chromosomal disorders are:
Down Syndrome – This syndrome results from an extra copy of the chromosome 21, in which mental retardation, abnormal facial features and medical problems such as heart defects occur. Children with Trisomy 21 (Down Syndrome) will have developmental and intellectual delays.
Trisomy 18 – Also known as Edwards Syndrome, this disorder results from an extra copy of the chromosome 18, and results in serious consequences for mental and physical development. When carried to term, fifty percent (50%) of infants will be stillborn, with mortality occurring more frequently in boys than in girls. Statistically, most infants die within the first year of life; however, a small number of adults – usually girls – are living well into their 20s and 30s, but with profound mental and medical delays which do not allow them to live independent lives.
The risk of having a child with a chromosomal defect increases as a woman ages. The chart below expresses the statistics as such, taking the mother’s age into consideration:
Age Down Syndrome Any Chromosomal Disorder
The purpose of testing is to determine if you are at an increased risk of having a baby with chromosomal abnormalities. The decision to test is optional and is completely your decision.
Cystic Fibrosis Carrier Screening
Cystic Fibrosis (CF) is the most common inherited disease of children and young adults. It primarily involves the respiratory, digestive and reproductive systems. Some people are mildly affected and may live into their 30s, but individuals with severe disease state may die in childhood. CF does not affect intelligence.
In the United States, 1 in 30 people are carriers of CF, but this number varies by ethnicity. If both parents are carriers, there is a 1 in 4 chance (25%) of having a child born with CF.
The purpose of testing is to determine whether you are a carrier of CF. This test does not detect all carriers of CF. You may be a carrier of CF even if no one in your family is affected and even if you already have healthy children.
If you are a carrier, testing your partner will help you learn more about the possibilities or odds that your baby could have CF. If one parent is a carrier and the other is not, it is still possible that the baby will have CF, but that chance is less than one percent (1%). If both parents are carriers, prenatal testing is highly recommended. Testing is available to determine whether or not the baby has inherited the abnormal CF gene.
Fragile X Syndrome Carrier Screening
Fragile X Syndrome is the most common inherited cause of mental retardation. It involves developmental delay, mental retardation, autism and hyperactivity. It primarily affects boys. Women who are carriers are at risk to have a child with mental retardation.
In the US, approximately 1 in 260 women are carriers. If a mother is a carrier, there is a fifty percent (50%) chance of having a child with Fragile X Syndrome.
The purpose of testing is to determine if you are a carrier. This test does not detect all carriers of Fragile X. You may be a carrier of Fragile X even if no one in your family is affected and even if you already have healthy children.
If you are a carrier, prenatal testing is available to find out whether or not the baby has inherited the abnormal gene.
Spinal Muscular Atrophy (SMA) Carrier Screening
SMA is the most common inherited cause of early childhood death. It destroys nerve cells that affect voluntary movement. The most common form of SMA affects infants in the first few months of life and can cause death between 2-4 years old. Infants with SMA have problems breathing, swallowing, moving, crawling and walking. Less commonly, the disease presents later, and people with delayed onset of SMA can survive into adulthood. SMA does not affect intelligence. There is no cure or treatment for SMA.
In the US, the carrier rate varies by ethnicity and range from 1 in 47 to
1 in 72. If both parents are carriers, there is a 1 in 4 or twenty-five percent (25%) chance to have a child born with SMA.
The purpose of testing is to determine whether you are a carrier of SMA. This test does not detect all carriers of SMA. You may be a carrier of SMA even if no one in your family is affected and even if you already have healthy children.
If you are a carrier, testing your partner will help you learn more about the chance or odds that your baby could have SMA. If one parent is a carrier and the other is not, it is still possible that the baby will have SMA, but that chance is less than one percent (1%). If both parents are carriers, prenatal testing is highly recommended. Testing is available to determine whether or not the baby has inherited the abnormal SMA gene.
Additional Testing Options
Non-invasive Genetic Testing
Non-invasive genetic testing consists of blood work done after 10 weeks of pregnancy to detect Trisomy 21, Trisomy 18, and Trisomy 13. Blood testing yields results with an over 98% accuracy rate. Currently, this type of testing is covered by most insurance plans for patients who are older than 35, have had a previous child with a chromosomal defect, or who have presented with an abnormal screening test during the current pregnancy.
This testing combines the results of a special ultrasound test, called the Nuchal Translucency Screening. This test is performed between 11 and 14 weeks of pregnancy, and involves blood being taken on two occasions in the pregnancy. This test looks for only limited chromosomal abnormalities. Sequential screening will not give a definitive result. It will only adjust the age-related risk. This is the recommended test for patients less than age 35 and who present to us without other risk factors.
Amniocentesis or Chorionic Villus Sampling (CVS)
These tests are invasive and involve inserting a needle into the uterus to obtain a sample of amniotic fluid a or biopsy of the placenta. These tests will give a definitive answer, but there is a miscarriage risk associated with these tests. Due to the availability of non-invasive testing, the use of these tests has declined in recent years.
If you have any questions and concerns about your risks related to genetic testing, speak with your doctor. Ask questions, and learn as much as you can. The more you know, the better decisions you can make for you and your family.