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Author:
Palak Thakkar
- >> Post Created: September 20, 2020
- >> Last Updated: December 11, 2024
Medically Reviewed by: Dr. Veena Shinde (M.D, D.G.O, PG – Assisted Reproductive Technology (ART) from Warick, UK) Mumbai, India
Table of Contents
All first time mothers (and even experienced ones) are bombarded with a plethora of information about what to do and what not to do. Parents, doctors, friends, colleagues, and even strangers are ready to share their expertise regarding your pregnancy.
There are a few people’s advice that you can easily ignore, but the one person you should never ignore is your doctor.
Your pregnancy is divided into trimesters of 3 months each, and each trimester comes with its own set of instructions, tests, and requirements, so that you can ensure your pregnancy is progressing well.
For easing the journey for all you would be mothers, we are providing you with information regarding the First Trimester Screening that you would need to go through, its importance, and all you need to know about your ‘First Trimester Screening.’
Types of screening
The screening tests conducted during your pregnancy will provide you with information regarding the potential risks of having a baby with genetic disorders. The tests can be broadly divided into carrier screening tests and prenatal genetic screening tests.
Carrier screening is generally done by couples before they are even planning to have a baby, although the tests can also be conducted during the pregnancy. The tests are mainly conducted using blood samples or tissue samples (usually cheek swabs). These tests help determine if a person is a carrier of any inherited disorders like sickle-cell anemia, cystic fibrosis, etc.
Both the parents have to be carriers for the baby to develop the disorder. Carrier screening beforehand can help you and your partner take the necessary steps to avoid passing on the disorder to your baby.
Prenatal genetic screening tests are conducted on blood samples collected from a pregnant woman or through ultrasound examinations. These tests can help identify certain genetic disorders that your baby might be at a risk of having. It can also help identify defects in the heart, abdomen, skeleton, neural tube defects (brain and spine defects), etc. This article covers these prenatal genetic screening tests, more specifically first trimester screening tests.
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What is first trimester screening?
The first trimester screening is a combination of ultrasounds and blood tests conducted on the mother between week 1 – week 12/13 of her pregnancy.
The first trimester screening combines the results of the following tests:
- Nuchal translucency test, which is an ultrasound examination. Through the ultrasound, the area in the back of the baby’s neck is examined. An increase in the thickness of this area is an early sign of genetic disorders like Down Syndrome.
- Blood tests for beta human chorionic gonadotropin (beta-hCG) and pregnancy-associated plasma protein A (PAPP-A). Beta-hCG is produced in the placenta and its levels can be related to certain genetic abnormalities. PAPP-A is a protein present in the blood and its low levels can also be related to certain birth defects.
- NIPT (Noninvasive prenatal testing) or sometimes also called as NIPS (Noninvasive prenatal screening) is a method of determining the risk that the fetus will be born with chromosomal anomalies.
First trimester screening is generally done between weeks 11 and 14 of pregnancy. When the pregnancy approaches the end of the 3-month mark (usually between 11th to 14th week of pregnancy), i.e. towards the end of the first trimester, the woman may need to undergo all the above tests to help doctor identify the risk of the baby being born with any birth defect. Again this is basis what your doctor may prescribe for you.
When the results of these tests are combined, they are collectively called as the first trimester screening for genetic disorder.
First trimester screening is also referred to as combined first trimester screening, first trimester screening for birth defects or simply the combined screening.
These tests can help the doctor determine the chances that your baby has – of being born with certain genetic disorders like Down Syndrome (Trisomy 21), Edwards Syndrome (Trisomy 18), Patau Syndrome (Trisomy 13), etc.
The first trimester screening cannot give a confirmation of the disorder in your child, it is only a risk assessment. A diagnostic test needs to be performed to confirm the presence of the disorder.
How are the first trimester screening tests conducted and do they hurt?
Nuchal translucency test: For the nuchal translucency test, the doctor or the ultrasonographer will spread a gel like substance on your abdomen. They will use a transducer (a device that is designed to send and receive sound waves) and gently move it over the applied gel on your abdomen.
The sound waves that the device sends into the body will be reflected and send back which will be digitally converted into images. These images can be seen in the monitor attached to the machine.
With the help of these images, the doctor can measure the thickness on the back of the baby’s neck area to determine the possibility of Down Syndrome. This procedure requires a specially trained radiologist and equipment and, therefore, this procedure is not available everywhere.
The ultrasound can be performed transvaginally, i.e. a probe is sent through the vagina instead of from the outside on the abdomen as described above.
Please Note: For the nuchal translucency test, you may be advised to have a full bladder for better results in the ultrasound.
Blood test: The blood test for the first trimester screening is no different from your other regular blood tests. A doctor or a health care professional will remove a sample of your blood with the help of a syringe or a prick on your finger. The collected blood sample will be sent to a lab for testing the beta-hCG and PAPP-A levels in your body. It is as simple as that.
Other than a possible minor bruise on your arm due to the blood test, there are no other known physical risks associated with the above tests. It is completely safe for you and your baby.
Understanding the First Trimester tests results
The results from the ultrasound along with the results of the blood tests are combined, and your age and other factors are added in to give a calculated assessment for you and your baby.
If your test results are positive, it means you have a higher-than-average chance of having a baby affected with Down Syndrome or other genetic disorders. Similarly, if your test results are negative, it means your baby probably does not have any genetic disorders.
But a negative test result does not guarantee that your baby will not have any birth defects. As these tests are only accessing the risk of the baby having any disorders, they are not diagnostic tests that can give confirmed results.
The results may also be presented to you in the form of numbers. Don’t get confused; it is just another way of portraying the results. For example, if you have done any blood test and checked the result, you will always see an acceptable range of numbers given and anything below or above this range can be a matter of concern.
Similarly in these tests, the cut-off may be 1 out of 200, i.e. your baby has a 1 in 200 chance of being at risk of being born with a genetic disorder. So the doctors will suggest you have a positive result if your number is below 200. On the other hand, if your results are 1 out of 300 or above, then the doctors will suggest a negative result.
How accurate are the first trimester test results?
As I have emphasized all throughout the article that the first trimester screening tests can only provide you with a risk assessment. A positive test is not a guarantee that your baby will have a birth defect and a negative test is not a guarantee that your will not have a birth defect. The accuracy of these tests is based on how often they are able to successfully identify the genetic disorders.
The nuchal translucency test on its own can correctly identify Down Syndrome in 64–70 out of 100 cases who are affected with the disorder. This means that it fails to identify 30–36 out of 100 cases affected with the disorder.
The first trimester screening, i.e. the ultrasound along with the blood tests, correctly identifies Down Syndrome in 82–87 out of 100 cases affected with the disorder. This means that it fails to identify 13–18 out of 100 affected cases with the disorder.
The integrated test, i.e. the first trimester screening plus the quad screening that is conducted in the second trimester, correctly identifies Down Syndrome in 96 out of 100 cases affected with the disorder. This means that it fails to identify 4 out of 100 affected cases with the disorder.
Sometimes the first trimester screening may provide a positive result but the baby is born completely healthy without any birth defects, such a case is called a false-positive test result.
Similarly, sometimes the first trimester screening may provide a negative result but the baby is born with a genetic disorder, such a case is called a false-negative test result.
A false-positive result can lead to unnecessary stress and further potentially painful testing.
Advanced diagnostic tests
If your first trimester screening is positive, the doctor may advice you to go for further tests to confirm whether the baby has any genetic defects. The first trimester screening is only the risk assessment, confirmed results can only be obtained after diagnostic tests.
The most widely used diagnostic tests are amniocentesis and chorionic villus sampling (CVS). The doctor may recommend either one of the tests to confirm the baby’s genetic disorder. We have described all the diagnostic tests as follows:
Amniocentesis: It is a procedure in which some of the amniotic fluid along with cells are withdrawn with the help of a needle from the sac that holds the fetus. This test can help diagnose genetic disorders like Down Syndrome and also neural tube defects (NTDs) like spina bifida (first trimester screening cannot detects NTDs). As it is an invasive procedure, it does have a minor risk of miscarriage or even a rare injury to the fetus.
Chorionic villus sampling (CVS): It is a procedure in which cell samples are taken from the placenta and tested for birth defects. This procedure can help diagnose genetic disorders like Down Syndrome. Just like amniocentesis, CVS also poses a minor risk of miscarriage or even a rare injury to the fetus.
Cell-free fetal DNA (cffDNA): This tests does not require cells and, therefore, is non-invasive. All it requires is a blood sample from the mother. The fetal DNA present in the bloodstream of the mother is then examined to determine whether the fetus has any chromosomal abnormalities like Down Syndrome, Edwards Syndrome, Patau Syndrome, etc.
If the result for this test is negative, it eliminates the need for other invasive tests that can be risky for the baby. If the result is positive, you will still need to conduct amniocentesis or CVS to confirm the birth defect. As this test is fairly new, it may not be available everywhere and many insurance companies may not cover the cost for performing it.
Other than the above tests that can be performed during the first trimester, the maternal serum screen performed during the second trimester can also help detect the genetic disorders.
What else you need to know about First Trimester Screening?
The results of the tests are dependent on the ultrasound techniques and the determination of correct gestational age of the fetus. The results of the first trimester screening can be either falsely high or low if the gestational age of the fetus has not been determined accurately.
If you are pregnant with twins, triplets or more, then the calculation of the risk of genetic disorders like Down Syndrome can be difficult, as the amount of beta-hCG and PAPP-A levels are high in the body due to more babies. The nuchal translucency ultrasound is conducted for each baby separately and, therefore, it will not have a problem in the analysis. A woman who is pregnant with multiple babies should consult with her healthcare provider to understand her options.
Final thoughts
At the end, whether you want to perform the first trimester screening and any further diagnostic tests is completely dependent on you. Nobody can force you to do anything without your permission. To decide whether to know about birth defects beforehand can be a difficult choice for many parents.
You need to think what this decision would mean to you and your entire family.
Deciding to perform the first trimester screening tests can help you in the following ways:
- If the birth defect has been identified early, then it can be rectified with a potential intervention like the fetal surgery for spina bifida, you can help your baby to grow up without the defect.
- You are better prepared to manage a kid with special needs. You can start planning and reading about how to manage a child with special needs.
- A special needs child may need certain lifestyle changes from your end as well. Addressing these lifestyle changes can help you prepare in advance.
- You have to support the child, but you may also need support from time-to-time. Finding support groups in your area will help you understand your situation from parents who are already taking care of a child with special needs.
- If you and your partner feel that maybe you are not equipped to support a child with special needs, knowing beforehand can also help you decide whether to carry the baby to full-term.
If you are still undecided whether to do first trimester screening, you can talk to a genetic counselor. The counselor will inform you about the pros and cons of the first trimester tests along with the kind of information you will gain through them about your growing fetus. They can even support you and find the necessary help that you might need for the first trimester screening.
Healthy Pregnancy!
