Before we talk about the available testing options, we need to define the difference between the two categories of available tests: screening tests vs. diagnostic tests.
A screening test gives us information on the risk of a pregnancy having a specific problem.
Another way to think about it: “What are the chance/odds that a problem may exist?” While an abnormal result on a screening test may be concerning, it only signals a potential problem which may require further testing to follow up. In order to have a definitive answer it is necessary to perform a diagnostic test. This type of test will let you know 100% if there is an abnormality, but is an invasive test that requires a procedure to collect either amniotic fluid or a small sample of cells from the placenta.
We offer this testing to all of our patients. This is a personal decision that you and your family may want to consider. Some women will want to do screening tests initially, because it is not invasive (there is no risk to the pregnancy). Although if this result shows that your pregnancy is at increased risk, we will recommend you proceed with a CVS or amniocentesis (diagnostic test) to get a final answer. Other women, especially those at higher risk including those over the age of 35 or who have had a history of a genetic problem in a previous pregnancy, may want a diagnostic test done initially. It is also acceptable for you not to undergo any testing, if you choose.
First Trimester Screening
In the first trimester, screening involves blood work and an ultrasound examination of the fetus. This may be done alone or in combination with further testing at a later date. It is usually performed at 11-14 weeks of pregnancy. Measurement of chemical markers in the mother’s blood combined with an ultrasound measurement of the thickness of the back of the fetal neck (“nuchal translucency”) help detect those pregnancies at increased risk for Down syndrome or other chromosomal problems. This test will detect the majority (82-87%) of Down syndrome, but may not detect all cases.
Second Trimester Screening
In the second trimester, the level of four of substances in your blood may be measured to screen for Down syndrome, trisomy 18, and neural tube defects. This test is typically performed between 15-20 weeks of pregnancy. This test is a less sensitive than the first trimester test, detecting 70-81% cases of Down syndrome. A part of this test can be performed to look only for neural tube defects (problems with the incomplete closure of the fetal spine), known more commonly as “spina bifida”. It can detect around 80% of these abnormalities. If you decide to do the first trimester screening, this part only will be performed.
The integrated test (first trimester ultrasound measurement of nuchal translucency thickness and maternal serum pregnancy associated plasma protein-A (PAPP-A) plus second trimester quadruple markers) is the overall best screening test for Down syndrome. It allows us to identify the highest percentage of affected fetuses with the lowest false positive results.
Chorionic Villus Sampling (CVS)
This diagnostic test is usually performed between 10-13 weeks. If your want to pursue this type of testing, we will refer you to a highly trained specialist. A CVS allows you to know the gender and exact number of chromosomes a fetus has, which will provide information about specific genetic disorders (i.e. Down syndrome). This test is performed by taking a sample of a few cells from part of the developing placenta under ultrasound guidance, either by a thin needle through the abdomen or a thin tube in the vagina and through the cervix. Because this test involves invasive methods, it does carry a potential risk of miscarriage.
This diagnostic test is similar to a CVS, but done at a later point of time in a pregnancy. It is typically performed between 15 and 20 weeks gestation, but taking a sample of amniotic fluid through a needle into the uterus. It is also done with ultrasound as a guide and also has a risk of miscarriage. This test is typically done for similar reasons as a CVS to test for certain birth defects and genetic conditions.
CYSTIC FIBROSIS CARRIER SCREENING
Cystic fibrosis (CF) is a genetic (inherited) disease. About 30,000 children and adults in the United States have the disorder. Cystic fibrosis severely affects breathing and digestion. It is caused by an abnormal gene that makes the body produce thick mucus in the lungs. This mucus promotes infections that are often life threatening. In the pancreas, similar thick secretions can lead to serious problems with food absorption.
CF carrier testing is a blood test that checks to see if parents-to-be have (carry) the abnormal gene that causes CF. The test can help determine if you’re at increased risk for having a child with CF.
The only way to get CF is to have two genes that cause CF—one from your mother and one from your father. This means that both parents are CF carriers. A CF carrier has only one CF gene and has no CF symptoms. If only one parent from a couple is a CF carrier, none of the children will have CF. But there is a 50-50 chance that each child will be a symptomless carrier. When both parents carry the CF gene, there is a 25% chance (1 in 4) that their child will have CF.
Approximately 1 in 30 Americans is a symptomless carrier of the CF gene. If you have a family history of CF, you’re more likely to carry the gene than someone from an unaffected family. The risk is increased if you’re of Caucasian background.
The American College of Obstetricians and Gynecologists (ACOG) recommends that health care providers make the CF carrier screening test available to all couples. Deciding whether or not to have the test is your own personal choice. Talk it over with your partner and with your health care provider and get as much information as you need to decide what’s right for you and your baby. This test may not be covered by your insurance. If this is of concern to you, please check with your insurance carrier and talk to our office regarding the potential cost of this test.
Spinal Muscular Atrophy Carrier Testing
Spinal muscular atrophy (SMA) is another autosomal recessive disorder (like previously described for cystic fibrosis). If affected with this condition, a person may have degeneration of some nerves in the spinal cord. This can lead to muscle weakness and ultimately may even cause death from respiratory failure. The severity of the disease can vary due to different subtypes of the disease. The most common form leads to paralysis and early childhood death, but there are milder forms where a person could live into adulthood with fewer limitations. Unfortunately, the most common variations tend to be the most serious and there is no way to predict the severity of disease before it occurs.
About 1 in 40 to 1 in 50 people are carrier of the SMA gene and this is the same for all racial and ethnic groups. We have the ability to test to see if you are a carrier for this disease. Given the way this condition is inherited, even if your testing is “normal” there is still a very small chance that a child could end up affected with the disease.
CORD BLOOD BANKING AND DONATION
Cord blood is the blood that remains in the umbilical cord and placenta after your baby has been delivered and the umbilical cord is cut. This is normally discarded with the placenta after birth, but you have the option to collect this blood to store for your own potential use or to donate to others to use. The reason some people choose to save this blood is because it is rich in stem cells, which are the starting point from which all the body’s tissues and systems develop. Since these unique cells have the ability to change into other types of cells in the body, they have the potential to treat or cure some common diseases. Currently there are over 70 diseases that they are used to treat, including blood cancers, other cancers, other blood disorders, and immune diseases. Research is also being done on the ability of these cells to treat common medical problems, such as diabetes and heart disease.
The cells that are collected are genetically unique to your child and your family. You have the option to save these cells in case your child or other family members may need treatment with stem cells in the future. There are private cord blood banks that will help you collect these cells, process them, and store them for future use. Of course, there is a onetime collection and processing fee, as well as a yearly storage fee. If you choose to privately bank your baby’s cord blood, we recommend using a reputable bank, such as CBR (Cord Blood Registry) or ViaCord.
There is also the option of public donation, which is a free process. This means that the blood goes to a public blood bank to be used by anyone who may need it in the future (as long as they are a “match” for the cells). If you donate the cord blood, you will not personally have access to these cells if your family has a need for stem cells.
If you have questions regarding whether cord blood collection is right for you please talk with your doctor and feel free to look at the following web sites for more information.
All expectant parents should View this Video on Cord Blood Banking