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The first trimester screening is one of the most accurate methods of non-invasive screening – according to an article published in the New England Journal of Medicine (published on November 2005). According to this report, about 85 percent of babies with the chromosomal abnormalities are successful detected with this test. What else you should know?
Read also the previous posts about normal and abnormal cramping in the first trimester of pregnancy and nutrition tips for your early pregnancy, before continuing!
Though this screening test has been available in the U.S since before 2005, but its effectiveness in detecting early chromosomal abnormalities has recently confirmed.
What is the first trimester screening – why you need to do it?
What is the first trimester screening – why you need to do it?
It is an optional prenatal test (noninvasive evaluation) that uses the combination of ultrasound evaluation of the fetus and a maternal blood test.
It is aimed to provide early information about the risk of specific chromosomal abnormalities, particularly such as Trisomy-18 (‘Edwards-syndrome’) and Trisomy-21 (‘Down syndrome’). But it is usually not intended to evaluate and gauge the risk of spina bifida (a kind of neural tube defect).
Trisomy-21 can lead to lifelong impairments in social and mental development. It also can be potential to cause lifelong impairments in various physical symptoms. And for Trisomy-18, it can cause more severe delays and even it is often fatal by age 1!
Before performing the test, it’s important for you to understand any important issues associated with the test. This is intended to help eliminate some of the anxiety which may affect the result of the test.
The first trimester screening is not only focused to the result of your blood test and ultrasound scanning test. In other words, there are also other factors that affect the test-result. To get the accurate result, doctors still need to compare a number of different variables (such as your age, or even your ethnicity if necessary, etc).
And one thing you should completely understand the test is not purposed to diagnose a problem, but it is more focused to gauge the risk of a pregnant woman of delivering a baby with specific genetic disorders (such as Edwards and Down syndrome).
When and how to do it?
As the name suggests, the test is typically done in the weeks 11 -14 of pregnancy (weeks in the trimester of your pregnancy). But there is also a form of this test that can be done earlier (such as about 9th week of pregnancy)!
Because this kind of test can be done earlier than other prenatal screenings, you will get the result of the test earlier. And this is beneficial to give you and your doctor more time to determine the choices of medical treatment, further diagnostic tests, or even the course of your pregnancy.
For instance, if the result of test shows that your pregnancy are at high risk of Down syndrome - you and your doctor will have more time to prepare the best steps.
Is there anything you should do before performing the test? In general, there is no anything special that you should prepare for the test. Even your doctor may still allow you to eat /drink normally before the test. In general, first trimester screening has 2 major procedures:
Blood test
It is used to measure two major hormones associated with pregnancy (PAPP-A ‘pregnancy-associated plasma protein-A’ and hCG ‘human chorionic gonadotropin’). This step may take about 5-10 minutes for drawing sample blood from your body.
To take a sample of blood, doctor uses a special needle that can be inserted into a vein of arm. Your sample blood then will be closely analyzed in the laboratory. Overall this test is pretty simple - even you may be allowed to return to you daily activities immediately after the test.
Ultrasound imaging test!
It is used to evaluate and measure fluid beneath the skin at the back of the baby’s neck (nuchal translucency). This test is commonly performed by a perinatologist /ultrasound specialist, and it usually takes about 20-40 minutes.
During the test, you will be asked to lie on your back. Then the specialist will place a special slender in your genital area to send out the appropriately sound waves.
These sound waves can result a lot of reflections from the structure inside the body. Then these reflected sound waves will be gathered and then will be converted into a more detailed picture on a monitor. And doctor then can use this picture to analyze the fluid in the nuchal translucency. Typically, the result of the test can be made within a week of the testing.
Increased fluid in the nuchal translucency may signal the high risk of chromosomal abnormalities. With other factors (such as low /high level of PAPP-A & hCG, and also the maternal age), doctors can evaluate the overall risk factors to gauge the risk of chromosomal abnormalities.
What are the side effects?
Some people worry about the risk of pregnancy complications or even miscarriage, but these side effects are still not confirmed. In other words, there are no known side effects of this test, except you may feel discomfort when drawing blood for blood test.
Overall, experts believe that there is no risk of pregnancy complications after performing the first trimester screening. Consult more with your doctor if you in doubt with this issue!
How about with the accuracy of the first trimester screening?
As mentioned before, the accuracy of the test is about 85 percent – and with a false positive rate of about 5 percent. The following is the explanation of the statistic according to a research published in NEJM (the New England Journal of Medicine):
- An abnormal level (a positive result) will be pointed to about 5 percent of all normal pregnancies. This means the result of test is positive but the newborn doesn’t actually have chromosome abnormalities, such as Down syndrome.
- About 85 out of 100 babies affected by genetic disorders /abnormalities will be successfully identified. This means from about 100 pregnancies that have positive test-result, 85 of them actually delivery babies with genetic disorders.
The results – abnormal and normal range of first trimester screening!
Once again, the first trimester screening is not intended to diagnose a problem! It is more focused to gauge your pregnancy’s chance of delivering a newborn with certain genetic disorders (such as Edwards or Down syndrome).
In other words if you have a high-risk result, this cannot be used to tell you that you will definitely deliver a baby with genetic disorder. And if you have a low-risk result, this also doesn’t guarantee that you will not delivery a baby without Down or Edwards syndrome!
For the result of test, your genetic counselor usually will give the number of risk that can gauge your pregnancy into ‘normal’ or ‘abnormal’ category. In general, the result of test is considered negative (normal or low risk) if the risk is lower than 1/300.
On the other hand, if you get the number of risk between 1/100 –to- 1/300, it is considered abnormal (positive or high risk)! For this case, you genetic counselor usually suggests the further testing.
