Nuchal Translucency Calculator
Understand nuchal translucency screening results.
For Educational Purposes Only
Using Gestational Age from CRL:
~43th percentile
The measured nuchal translucency is within the normal range.
The first trimester of pregnancy is a time of rapid development and important health screenings. One of the key screenings offered to expectant parents is the Nuchal Translucency (NT) scan. This non-invasive ultrasound is a vital tool for assessing the risk of certain chromosomal abnormalities in the developing fetus. This guide is designed to explain what the NT scan is, what it measures, how the results are interpreted, and what the next steps might be.
The NT scan is a screening tool, not a diagnostic test. It provides a risk assessment, not a definitive "yes" or "no" answer. This guide is for educational purposes only and should not replace consultation with a healthcare provider or genetic counselor.
What is Nuchal Translucency?
"Nuchal" refers to the back of the neck, and "translucency" refers to a clear or fluid-filled space. The Nuchal Translucency is the normal, small collection of fluid under the skin at the back of a fetus's neck.
The NT scan uses ultrasound to precisely measure the thickness of this fluid-filled space. The measurement is taken when the fetus is between 11 and 14 weeks of gestation. It has been observed that fetuses with certain chromosomal conditions, such as Down syndrome (Trisomy 21), Edwards syndrome (Trisomy 18), and Patau syndrome (Trisomy 13), as well as some congenital heart defects, tend to accumulate more fluid at the back of the neck during this specific developmental window. Therefore, an increased NT measurement can be a marker for a higher risk of these conditions.
The "Combined" First Trimester Screening
The NT measurement is powerful, but it's rarely used in isolation. To provide the most accurate risk assessment, it is combined with other data points in what is known as the "First Trimester Screen" or "Combined Test."
The components of this combined screening are:
- The NT Ultrasound Measurement: The thickness of the nuchal translucency in millimeters.
- Maternal Blood Test: A blood sample is taken from the mother to measure the levels of two specific pregnancy-related proteins:
- hCG (human chorionic gonadotropin): Abnormally high or low levels can be associated with chromosomal issues.
- PAPP-A (pregnancy-associated plasma protein-A): Low levels of PAPP-A are also associated with an increased risk.
- Maternal Age: A woman's age is a significant factor, as the baseline risk of having a baby with a chromosomal abnormality increases with age.
A sophisticated software program takes all of these results—the NT measurement, the two blood protein levels, and the mother's age—and uses a complex algorithm to calculate a single, personalized risk score for specific conditions.
Understanding Your Risk Score
The result of the First Trimester Screen is given as a probability or a ratio. For example, you might be told your risk for Down syndrome is "1 in 2,000" or "1 in 150."
- Screen-Negative (Low Risk): This means your calculated risk is lower than the established cutoff (e.g., lower than 1 in 250 or 1 in 300, depending on the lab). A screen-negative result is very reassuring and means it's highly unlikely that your baby has one of the conditions screened for. However, it does not completely eliminate the possibility.
- Screen-Positive (High Risk): This means your calculated risk is higher than the established cutoff. **It is crucial to understand that this does not mean your baby has a problem.** It simply means that your risk level is high enough to warrant the offer of further, more definitive testing. The majority of women who receive a "high-risk" result go on to have healthy babies. An NT measurement above the 95th percentile is typically a key driver of a high-risk result.
What Happens After a High-Risk Result?
If your screening comes back positive, your healthcare provider or a genetic counselor will discuss your options for diagnostic testing. Unlike screening tests, diagnostic tests can provide a definitive "yes" or "no" answer about whether a chromosomal condition is present.
The main options include:
- Non-Invasive Prenatal Testing (NIPT): This is another, more advanced screening test done via a simple blood draw from the mother. It analyzes fetal DNA fragments in the mother's blood and is highly accurate for detecting common trisomies. It is often the next step after a high-risk First Trimester Screen.
- Chorionic Villus Sampling (CVS): An invasive diagnostic procedure, usually done between 10 and 13 weeks, that involves taking a tiny sample of tissue from the placenta for genetic analysis. It carries a small risk of miscarriage.
- Amniocentesis: An invasive diagnostic procedure, usually done after 15 weeks, that involves taking a small sample of the amniotic fluid surrounding the baby for genetic analysis. It also carries a small risk of miscarriage.
The decision to undergo diagnostic testing is a deeply personal one. A genetic counselor can provide invaluable support, helping you understand the risks and benefits of each option so you can make the choice that is right for you and your family.
Enter values to see the results.
The first trimester of pregnancy is a time of rapid development and important health screenings. One of the key screenings offered to expectant parents is the Nuchal Translucency (NT) scan. This non-invasive ultrasound is a vital tool for assessing the risk of certain chromosomal abnormalities in the developing fetus. This guide is designed to explain what the NT scan is, what it measures, how the results are interpreted, and what the next steps might be.
The NT scan is a screening tool, not a diagnostic test. It provides a risk assessment, not a definitive "yes" or "no" answer. This guide is for educational purposes only and should not replace consultation with a healthcare provider or genetic counselor.
What is Nuchal Translucency?
"Nuchal" refers to the back of the neck, and "translucency" refers to a clear or fluid-filled space. The Nuchal Translucency is the normal, small collection of fluid under the skin at the back of a fetus's neck.
The NT scan uses ultrasound to precisely measure the thickness of this fluid-filled space. The measurement is taken when the fetus is between 11 and 14 weeks of gestation. It has been observed that fetuses with certain chromosomal conditions, such as Down syndrome (Trisomy 21), Edwards syndrome (Trisomy 18), and Patau syndrome (Trisomy 13), as well as some congenital heart defects, tend to accumulate more fluid at the back of the neck during this specific developmental window. Therefore, an increased NT measurement can be a marker for a higher risk of these conditions.
The "Combined" First Trimester Screening
The NT measurement is powerful, but it's rarely used in isolation. To provide the most accurate risk assessment, it is combined with other data points in what is known as the "First Trimester Screen" or "Combined Test."
The components of this combined screening are:
- The NT Ultrasound Measurement: The thickness of the nuchal translucency in millimeters.
- Maternal Blood Test: A blood sample is taken from the mother to measure the levels of two specific pregnancy-related proteins:
- hCG (human chorionic gonadotropin): Abnormally high or low levels can be associated with chromosomal issues.
- PAPP-A (pregnancy-associated plasma protein-A): Low levels of PAPP-A are also associated with an increased risk.
- Maternal Age: A woman's age is a significant factor, as the baseline risk of having a baby with a chromosomal abnormality increases with age.
A sophisticated software program takes all of these results—the NT measurement, the two blood protein levels, and the mother's age—and uses a complex algorithm to calculate a single, personalized risk score for specific conditions.
Understanding Your Risk Score
The result of the First Trimester Screen is given as a probability or a ratio. For example, you might be told your risk for Down syndrome is "1 in 2,000" or "1 in 150."
- Screen-Negative (Low Risk): This means your calculated risk is lower than the established cutoff (e.g., lower than 1 in 250 or 1 in 300, depending on the lab). A screen-negative result is very reassuring and means it's highly unlikely that your baby has one of the conditions screened for. However, it does not completely eliminate the possibility.
- Screen-Positive (High Risk): This means your calculated risk is higher than the established cutoff. **It is crucial to understand that this does not mean your baby has a problem.** It simply means that your risk level is high enough to warrant the offer of further, more definitive testing. The majority of women who receive a "high-risk" result go on to have healthy babies. An NT measurement above the 95th percentile is typically a key driver of a high-risk result.
What Happens After a High-Risk Result?
If your screening comes back positive, your healthcare provider or a genetic counselor will discuss your options for diagnostic testing. Unlike screening tests, diagnostic tests can provide a definitive "yes" or "no" answer about whether a chromosomal condition is present.
The main options include:
- Non-Invasive Prenatal Testing (NIPT): This is another, more advanced screening test done via a simple blood draw from the mother. It analyzes fetal DNA fragments in the mother's blood and is highly accurate for detecting common trisomies. It is often the next step after a high-risk First Trimester Screen.
- Chorionic Villus Sampling (CVS): An invasive diagnostic procedure, usually done between 10 and 13 weeks, that involves taking a tiny sample of tissue from the placenta for genetic analysis. It carries a small risk of miscarriage.
- Amniocentesis: An invasive diagnostic procedure, usually done after 15 weeks, that involves taking a small sample of the amniotic fluid surrounding the baby for genetic analysis. It also carries a small risk of miscarriage.
The decision to undergo diagnostic testing is a deeply personal one. A genetic counselor can provide invaluable support, helping you understand the risks and benefits of each option so you can make the choice that is right for you and your family.