First Trimester Screening: An Early and Reassuring Look at Your Baby's Health

The First Trimester Screening is a crucial and highly recommended prenatal test that offers expectant parents the earliest possible look into the health and development of their baby. It is a completely non-invasive screening tool that is performed between the 11th and 14th weeks of pregnancy. The screening is a composite test, meaning it combines two different assessments performed on the same day: a specialized, high-resolution ultrasound called a Nuchal Translucency NT scan, and a simple blood test for the mother. The results of these two tests, along with several maternal factors like age, are then entered into a sophisticated computer algorithm to calculate a personalized risk score for specific chromosomal conditions, most notably Down syndrome Trisomy 21 and Edwards syndrome Trisomy 18.

This early assessment provides a powerful and reassuring data point for the vast majority of pregnancies, classifying them as low-risk and offering significant peace of mind to the parents. For the small percentage of pregnancies that are identified as high-risk, the screening is not a diagnosis; rather, it is a critical indicator that allows for timely and informed decision-making. It provides parents with the opportunity to pursue further, definitive diagnostic testing, such as a Chorionic Villus Sampling CVS or an amniocentesis, should they choose to do so. The First Trimester Screening is a cornerstone of modern prenatal care, empowering families with knowledge and options at the earliest possible stage of their pregnancy journey.

The Biological Markers of a Developing Pregnancy

To understand the profound accuracy of the First Trimester Screening, it is essential to explore the specific biological and anatomical markers that the test is designed to measure. These are subtle but significant indicators in the early development of a fetus that can provide powerful clues about its chromosomal health.

The Chromosomal Basis of the Conditions Screened

The test is designed to screen for aneuploidy, which is a condition where a fetus has an incorrect number of chromosomes. Humans normally have 46 chromosomes, arranged in 23 pairs.

Down Syndrome (Trisomy 21): This is the most common chromosomal abnormality. Individuals with Down syndrome have three copies of chromosome 21 instead of the usual two.

Edwards Syndrome (Trisomy 18) and Patau Syndrome (Trisomy 13): These are rarer and more severe conditions caused by an extra copy of chromosome 18 or 13, respectively.

The Ultrasound Markers: A Window into Fetal Anatomy

The Nuchal Translucency NT scan is a highly specialized ultrasound that looks for specific anatomical markers that can be associated with these conditions.

Nuchal Translucency NT: This refers to the normal, small collection of fluid that is present at the back of the neck of every fetus in the first trimester. In a fetus with a chromosomal abnormality, particularly Down syndrome, there is often an increased amount of this fluid, causing the NT measurement to be thicker than normal. This is thought to be related to subtle, early changes in the development of the fetal heart and circulatory system. The precise measurement of this tiny space is a key component of the screening.

The Nasal Bone: Extensive research has shown that a significant percentage of fetuses with Down syndrome have a delayed development of their nasal bone, making it either absent or not yet calcified and visible on an ultrasound between 11 and 14 weeks. The presence of a clearly visible nasal bone is a very strong and reassuring marker for a chromosomally normal baby.

Other Soft Markers: The specialist may also look at other subtle markers, such as the pattern of blood flow through a small vessel in the liver the ductus venosus and the function of the tricuspid valve of the heart.

The Biochemical Markers: Hormones in the Mother's Blood

The second part of the screening is the maternal blood test, often called the "Double Marker" test, which measures the levels of two specific pregnancy-related substances produced by the placenta.

Free Beta-Human Chorionic Gonadotropin (Free β-hCG): This is a subunit of the pregnancy hormone hCG. In pregnancies affected by Down syndrome, the level of free β-hCG is often significantly higher than the average for that gestational age.

Pregnancy-Associated Plasma Protein-A (PAPP-A): This is a protein produced by the developing placenta. In pregnancies affected by Down syndrome, the level of PAPP-A is often significantly lower than the average.

By combining the ultrasound findings with these biochemical markers and the mother's age, the screening algorithm can achieve a very high detection rate for Down syndrome, typically around 90-95%, with a low false-positive rate.

The Importance of an Early Assessment

The timing of the First Trimester Screening, between 11 and 14 weeks, is a critical window of opportunity in prenatal care.

Early Reassurance: For the majority of couples who receive a low-risk result, it provides profound peace of mind early in the pregnancy, allowing them to enjoy the journey with less anxiety.

Time for Decision-Making: For the small number of couples who receive a high-risk result, this early information is invaluable. It provides them with the maximum amount of time to process the information and to consider their options for further, definitive diagnostic testing.

Informed Choices: If a couple chooses to proceed with a diagnostic test after a high-risk screen, the early timing allows them to opt for a Chorionic Villus Sampling CVS, a procedure that can be performed between 11 and 14 weeks and provides a definitive answer within the first trimester. This gives a family more time and privacy to make any personal decisions about the management of the pregnancy.

Anatomical Preview: The NT scan also provides an excellent early look at the baby's basic anatomy, and in some cases, it can detect major structural abnormalities that are not related to chromosomes.

Patient Stories

"Being pregnant for the first time after the age of 35, I was naturally quite anxious about the risk of chromosomal abnormalities. We had the First Trimester Screening at Fortis, and the experience was so reassuring. The fetal medicine specialist was incredibly thorough during the NT scan, taking the time to show us our baby on the screen, pointing out the normal nasal bone, and explaining the measurements. A few days later, we got the final report, which showed a very low-risk result. That test gave us the confidence and peace of mind we needed to truly enjoy the rest of our pregnancy." - Mrs. Anjali Desai, 36, Pune

"Our first pregnancy tragically ended in a miscarriage due to a chromosomal issue. For our next pregnancy, our gynaecologist strongly recommended the First Trimester Screening. The scan and the blood test were straightforward, but the wait for the results was filled with anxiety. When our doctor called to tell us that the screening had come back low-risk, it was the most emotional and wonderful news. It felt like we could finally breathe and start to get excited about our baby's arrival." - Mr. and Mrs. Vikram Rathore, expectant parents, Jaipur

Your Experience During the Screening Process

The First Trimester Screening is a two-part process that is coordinated to happen on the same day.

Part 1: The Nuchal Translucency NT Ultrasound

This is a detailed and specialized ultrasound scan that requires a highly trained and certified sonographer or fetal medicine specialist.

Preparation: You will be asked to arrive for your scan with a comfortably full bladder. This helps to lift the uterus up and provides a clearer view for the transabdominal ultrasound.

The Scan: You will lie down, and the sonographer will perform a standard transabdominal ultrasound, applying gel to your abdomen and using a transducer to get the images. The primary focus will be on getting a perfect, magnified, sagittal view of the baby's profile to precisely measure the nuchal translucency and to visualize the nasal bone. The scan itself typically takes about 20 to 40 minutes.

Part 2: The Maternal Blood Test

This is a simple blood draw.

The Procedure: A small sample of blood will be taken from a vein in your arm.

The Analysis: This blood sample is sent to the laboratory to measure the levels of Free β-hCG and PAPP-A.

The Final Result: Your Personalized Risk Score

The results of the ultrasound, the blood test, and your personal demographic information are all entered into a specialized software program. The software then calculates your individual risk for Trisomy 21, 18, and 13. This is not reported as a simple "positive" or "negative," but as a statistical ratio.

Low-Risk Result: A result is considered low-risk if the chance is lower than the screening cut-off, for example, 1 in 1000. This means that out of 1000 women with your exact same results, only one would have an affected baby. This is a very reassuring result.

High-Risk Result: A result is considered high-risk if the chance is higher than the screening cut-off, for example, 1 in 150. This does not mean your baby has a problem. It means that out of 150 women with your results, one would have an affected baby. While this places you in a higher-risk category, the vast majority of women with a high-risk screen will go on to have a healthy baby.

Navigating a High-Risk Result: The Next Steps

Receiving a high-risk result can be very stressful. It is essential to remember that it is not a diagnosis. The next step is a detailed session with your doctor or a genetic counsellor to discuss your options for definitive diagnostic testing.

Non-Invasive Prenatal Testing NIPT: This is an advanced screening blood test that analyzes fetal DNA circulating in the mother's blood. It is highly accurate for Down syndrome and can be a good next step for many women.

Chorionic Villus Sampling CVS: An invasive diagnostic test performed between 11 and 14 weeks that takes a sample of the placenta.

Amniocentesis: An invasive diagnostic test performed after 15 weeks that takes a sample of the amniotic fluid.
Both CVS and amniocentesis are the only tests that can provide a definitive, 100% accurate diagnosis of the baby's chromosomes.

Myths vs Facts

Myth	Fact
The First Trimester Screening is a test that can diagnose Down syndrome	This is a critical misconception. It is a screening test, not a diagnostic test. It can only tell you if you are in a low-risk or a high-risk category. It cannot diagnose a condition. A definitive diagnosis can only be made with an invasive test like a CVS or an amniocentesis.
If my screening is low-risk, my baby is guaranteed to be perfectly healthy	A low-risk result is extremely reassuring and means the chance of your baby having one of the conditions screened for is very low. However, it does not reduce your risk to zero. It also does not screen for all possible genetic conditions or physical birth defects.
The NT scan is just a routine ultrasound to see the baby	The NT scan is a highly specialized and technically demanding ultrasound that requires a certified operator and a high-resolution machine. The measurement of the nuchal translucency must be performed with extreme precision according to strict international protocols to be accurate.
The test is painful and risky for the baby	The First Trimester Screening is completely non-invasive and safe. It consists of a standard ultrasound and a simple blood draw from the mother's arm. It carries no risk of harm to the baby.

An Empowering First Step in Your Pregnancy Journey

The First Trimester Screening is a remarkable advancement in prenatal care that offers expectant parents the gift of early information and reassurance. It is a simple, safe, and powerful way to gain invaluable insight into the health of your developing baby at the earliest possible stage. By combining advanced ultrasound technology with biochemical markers, it provides a highly accurate assessment of your individual risk, allowing for a more personalized and informed approach to your entire pregnancy.

Knowledge is a powerful tool on the path to parenthood. Whether your screening provides the welcome news of a low-risk result or identifies the need for further discussion and planning, the information it provides is invaluable. We encourage all expectant parents to have a detailed conversation with their obstetrician or fetal medicine specialist about the benefits of this crucial early screening.

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FAQ's

Who should have a First Trimester Screening?

The First Trimester Screening is a voluntary test that is offered and recommended to all pregnant women, regardless of their age or personal risk factors. It provides the most accurate risk assessment available in the first trimester.
Is the screening covered by insurance?

As a standard and highly recommended part of modern prenatal care, the First Trimester Screening, including both the NT scan and the Double Marker blood test, is typically not covered by most comprehensive health insurance plans in India.
What is the best time to have the screening done?

There is a very specific window for this test. It must be performed when your baby's Crown-Rump Length CRL measures between 45 mm and 84 mm, which corresponds to a gestational age of approximately 11 weeks to 13 weeks and 6 days.
Can the test tell me the gender of my baby?

While it may be possible to determine the gender on the ultrasound at this stage, the primary purpose of the scan is a medical evaluation. In India, under the Pre-Conception and Pre-Natal Diagnostic Techniques PC-PNDT Act, the determination and disclosure of the sex of the fetus is illegal and is not practiced.
What if I miss the window for the First Trimester Screening?

If you are past the 14-week mark, you can no longer have an NT scan. Your doctor will then offer you a Second Trimester Screening, most commonly the Quadruple Marker test, which is a blood test performed between 15 and 20 weeks that also screens for Down syndrome and neural tube defects.
What does a "risk cut-off" mean?

The risk cut-off is a pre-determined threshold that is used to separate the results into "low-risk" and "high-risk" categories. This is typically set by national or international guidelines. For example, a common cut-off for Down syndrome is 1 in 250. Any result with a higher probability than this is flagged as high-risk.
Is the test accurate for twin pregnancies?

Yes, the screening can be performed for twin pregnancies, but it is more complex. The sonographer must measure the NT for each individual baby. The risk calculation is also more complex, especially for the biochemical markers. It is essential that the scan is performed by a specialist with experience in multiple gestations.
What happens after a high-risk result?

After a high-risk result, the most important step is a detailed session with a genetic counsellor. They will explain what the result means in detail and will discuss all of your options for further testing, from the advanced non-invasive NIPT blood test to the definitive diagnostic tests of CVS or amniocentesis, allowing you to make an informed choice that is right for you.