The American College of Obstetrics and Gynecology recommends that ALL patients, regardless of age, should be offered both antenatal screening and diagnostic testing for fetal chromosomal abnormalities.
What is being Screened?
Antenatal screening tests were designed to detect women who may be at higher risk of having a baby with chromosomal abnormalities like Trisomy 21 (Down Syndrome), Trisomy 13, Trisomy 18, and some other conditions. These tests are only used to identify an increased risk of fetal genetic abnormalities or certain birth defects, and do not actually diagnose a specific condition. (Trisomy 13 and 18 are genetic conditions that lead to severe birth defects. Babies with these conditions often miscarry, are stillborn, or pass soon after birth.)
What Screening Tests are Available?
- First Trimester Screen (sometimes called a “First” Screen)
- Second Trimester Maternal Serum Screen (sometimes called a “Quad” Screen)
- Alpha Fetoprotein (sometimes called the AFP).
- Free Fetal DNA
- Anatomy ultrasound for fetal evaluation is provided for all patients and can detect some genetic anomalies as well.
What is the First Trimester Screen?
This is an optional test designed to help determine if a woman is at higher risk of carrying a baby with Trisomy 21 (Down Syndrome), Trisomy 13/18. Currently this test is offered at one of our partnering maternal fetal medicine practices. It can be performed between 11 and 14 weeks of pregnancy. The test involves an ultrasound and a blood test.
The ultrasound looks at the fluid on the back of the baby’s neck, also called the nuchal translucency. A larger amount of fluid can sometimes be associated with the above conditions. The blood test checks for two proteins in the mother’s blood. If these protein levels differ markedly from average, there could be an association with the above conditions. The test takes into consideration the ultrasound and blood test together when providing results. We usually have the results within 3-7 days from the time the blood is drawn.
This test is slightly more accurate than the second trimester serum screen. It also has the advantage of being done earlier in the pregnancy. The detection rate for Trisomy 21 is 91% and for Trisomy 13/18 is 95%. This test has a 5% false positive rate.
Most insurance companies cover at least part of this test. The ultrasound and blood tests are billed separately. Please check with your insurance provider or our billing department if you have coverage questions.
What is the Second Trimester Maternal Serum Screen?
This is an optional test designed to help determine if a woman is at higher risk of carrying a baby with Trisomy 21 or Trisomy 13/18. It also can detect women at risk of a baby with a neural tube defect like Spina Bifida, open abdominal wall defect like Gastroschisis or Smith-Limli-Opitz syndrome. This is a blood test that is offered between 15 and 23 weeks of pregnancy, but is ideally performed in our office between 15 and 20 weeks. It checks four proteins in the mother’s blood. If the levels differ markedly from average, there could be an association with the above conditions. We usually have the results within 3-7 days from the time the blood is drawn.
The advantage of this test is that it is usually less expensive and screens for several conditions in one step. It is slightly less accurate than the first trimester screen. The detection rate for Trisomy 21 is 80%, for Trisomy 13/18 is 60%, and for Spina Bifida is 80%. This test, like the first trimester screen, has a 5% false positive rate.
What is the AFP test?
The AFP, or alpha fetoprotein, test is a blood test offered between 15 and 23 weeks. However, like the Second Trimester Maternal Serum Screen, it is ideally performed between 15-20 weeks of pregnancy. It helps detect those at risk of a baby with Spina Bifida or Gastroschisis. However, with the advent of quality ultrasound equipment, most cases of Spina Bifida can be found ultrasonographically. We usually have the results within 3-7 days from the time the blood is drawn.
What is Free Fetal DNA?
Interestingly, a small percentage of the DNA floating in your blood stream is from your baby. A brand new lab test is available as early as 10 weeks of pregnancy that can analyze the free fetal DNA and identify with near certainty if your baby has Trisomy 21, 13 or 18. If this test returns positive for one of these, we still recommend a confirmatory diagnostic test described below.
Can Ultrasound Alone Detect Down Syndrome (Trisomy 21)?
Unfortunately, Down Syndrome (Trisomy 21) cannot reliably be diagnosed with an anatomy ultrasound. In most instances, ultrasound findings concerning for Down Syndrome are only identified in 50% of the patients that eventually deliver a baby with Down Syndrome.
What if My Results Show an “Increased Risk”?
It is very important to remember that a test that returns as increased risk does NOT mean that your baby has one of the above conditions. You will, however, be offered further testing such as a very detailed ultrasound, free fetal DNA test, chorionic villus sampling, or amniocentesis.
Diagnostic or Definitive Fetal Testing
What Diagnostic Tests are Available?
Diagnostic testing samples fetal cells to determine the fetus’s actual chromosome make-up and to definitively confirm if the fetus is genetically normal. Testing options include:
- Chorionic Villus Sampling (CVS)
What is Chorionic Villus Sampling (CVS)?
This is a test done between 10 and 14 weeks of pregnancy where a very small sample of the placenta is removed through a small needle. The cells in this sample can be used to help determine if your baby has Trisomy 21, 13, or 18. The test does carry a small risk of miscarriage of about 0.5%.
What is Amniocentesis?
This is a test done after 15 weeks of pregnancy where a small needle is used to remove a small amount of the fluid from around the baby. The cells in this sample can be used to help determine if your baby has Trisomy 21, 13, or 18. The test does carry a small risk of miscarriage of about 0.2-0.3%.