US PREGNANCY NT SCAN - TWINS

A Nuchal Translucency (NT) scan is a highly specialized ultrasound that measures a tiny, fluid-filled space at the back of a developing baby's neck. This space is called the "nuchal translucency." In the context of a nuchal translucency scan twin pregnancy, this meticulous measurement is performed for each individual fetus.

During the first trimester, all babies have this small collection of fluid. However, extensive research has shown that an increased amount of fluid, leading to a larger NT measurement, can be an early marker or indicator for an increased risk of certain chromosomal conditions, such as Down syndrome, as well as some major congenital heart problems.

The scan's goal is to precisely measure this space in millimeters for Twin A and Twin B. These individual measurements are a critical piece of data used in combination with other factors to calculate a specific risk profile for each of your babies.

Types of Twin NT Scans

A critical piece of information determined during your early twin ultrasounds is chorionicity—whether your twins share a placenta. This fundamentally impacts how the pregnancy is managed and how the NT scan results are interpreted.

• Dichorionic Twins (Separate Placentas): When each twin has their own placenta and amniotic sac, they are genetically unique (like any siblings, unless they are identical twins who split very early). For these pregnancies, the risk for chromosomal conditions is assessed individually for each twin. Each baby will receive their own NT measurement and final risk score.
• Monochorionic Twins (Shared Placenta): When twins are identical and share a single placenta, their genetic makeup is the same. Therefore, the risk of chromosomal conditions like Down syndrome is generally considered the same for both babies. However, measurements are still taken for each twin individually. This is vital for monitoring for other conditions specific to monochorionic pregnancies, such as Twin-to-Twin Transfusion Syndrome (TTTS), where an unequal flow of blood between the babies can sometimes be indicated by differences in their NT measurements.

Our expert sonographers will meticulously assess several key markers for both Twin A and Twin B to ensure a comprehensive screening:

• Nuchal Translucency (NT) Measurement: The precise measurement in millimeters of the fluid-filled space at the back of the neck for each baby.
• Crown-Rump Length (CRL): A measurement from the top of the head to the bottom of the torso. This is used to confirm the exact gestational age of each baby, which is essential for interpreting the NT measurement correctly.
• Nasal Bone (NB) Assessment: The sonographer will check for the presence or absence of the fetal nasal bone in each twin. Its presence is a reassuring marker that lowers the calculated risk score.
• Fetal Heart Rate: The heart rate of each baby is measured and recorded.
• Chorionicity and Amnionicity: Confirmation of whether the twins share a placenta (chorion) and/or an amniotic sac (amnion).

There are several compelling reasons why the twin NT scan is a cornerstone of first-trimester care:

1. Early Risk Assessment: The primary reason is to get an early, individualized risk assessment for each baby for conditions like Down syndrome (Trisomy 21), Edwards syndrome (Trisomy 18), and Patau syndrome (Trisomy 13).
2. Accurate Pregnancy Dating: The CRL measurements taken during the scan provide the most accurate dating of your pregnancy.
3. Determine Chorionicity: As mentioned, identifying whether twins share a placenta is crucial for managing the remainder of the pregnancy and knowing what potential complications to monitor for.

When and Who Needs to Take a Twin NT Scan?

The twin NT scan is recommended for all women with a confirmed twin pregnancy. It is considered a standard, essential component of first trimester screening for twins.

The timing of this scan is extremely important and not flexible. It must be performed between 11 weeks and 13 weeks and 6 days of gestation. This specific window is critical for two main reasons:

1. Before 11 weeks, the babies are too small for an accurate measurement.
2. After 14 weeks, the fluid at the back of the neck is naturally reabsorbed by the baby's developing lymphatic system, making the measurement no longer a valid screening marker.

Booking your appointment within this window is essential for the accuracy and validity of the test.

Benefits of Taking the Test

The information gained from a twin NT scan provides significant benefits for expectant parents:

• Empowered Decision-Making: The results provide early information that empowers you and your healthcare provider to make informed decisions about your prenatal care, including whether further testing like NIPT or CVS is desired. [Link to: Non-Invasive Prenatal Testing (NIPT)]
• Peace of Mind: For the vast majority of pregnancies, the scan will return a low-risk result, offering valuable reassurance early on.
• Early Planning: In the rare case of a high-risk result, it allows for early consultation with specialists and access to support resources.
• Guided Pregnancy Management: Identifying the chorionicity of your twin pregnancy dictates the entire schedule of monitoring for the second and third trimesters, ensuring your babies get the appropriate level of care.

Illness Diagnosed with US Pregnancy NT Scan - Twins

To be perfectly clear, this scan does not diagnose illnesses. It is a highly effective screening tool that identifies pregnancies with an increased risk for certain conditions. A high-risk result prompts a discussion about more definitive diagnostic testing. The primary conditions screened for include:

• Trisomy 21 (Down syndrome)
• Trisomy 18 (Edwards syndrome)
• Trisomy 13 (Patau syndrome)
• Certain major congenital heart defects (which can also be associated with an increased NT measurement)

Preparation for your US Pregnancy NT Scan - Twins is simple. Following these steps helps our sonographers get the clearest possible images:

• Have a Full Bladder: You will likely be asked to drink 2-3 glasses of water about an hour before your appointment and avoid emptying your bladder. A full bladder helps to lift the uterus out of the pelvis, providing a clearer ultrasonic window.
• Dress Comfortably: Wear a comfortable, two-piece outfit (like pants and a top) that allows for easy access to your lower abdomen.
• Bring Documentation: Remember to bring your doctor's referral form and any reports from previous scans you may have had.

Pre-requisites

• A confirmed multiple pregnancy from a prior dating scan.
• A valid referral for the scan from your obstetrician or GP.

Best Time to Take the Twin NT Scan

We cannot overstate the importance of timing for this test. The twin NT scan must be performed when each baby's Crown-Rump Length (CRL) is between 45mm and 84mm. This a size that directly corresponds to a gestational age of 11 weeks to 13 weeks and 6 days. The test cannot be performed outside of this window.

Eligibility

Any pregnant individual with a confirmed twin or other multiple gestation pregnancy who is within the specified gestational age window (11 weeks to 13 weeks and 6 days) is eligible for the scan.

Procedure for Taking a Twin NT Scan

Understanding the nt scan procedure for twins can help you feel more relaxed and prepared for your appointment at Cadabams Diagnostics. Here is a step-by-step guide to what you can expect:

1. Check-in and Preparation: You will check in at reception and may be asked to change into a gown.
2. Positioning: You will be asked to lie down comfortably on your back on an examination table in our calm and private ultrasound room.
3. Gel Application: Our sonographer will apply a clear, water-based gel to your lower abdomen. This gel feels cool but is harmless and helps ensure good contact between your skin and the transducer, allowing the sound waves to travel effectively.
4. The Scan: The sonographer will gently press and move a small probe, called a transducer, over your abdomen. Images of your babies will appear on a monitor, which you will be able to see.
5. Taking Measurements: This is the most time-consuming part of the procedure for twins. The sonographer needs to find the correct viewing angle for each baby to take the precise NT, CRL, and other measurements. This can require patience, as babies move around and may be in different positions. They will carefully document all findings for Twin A and Twin B.
6. Duration: Because two babies are being meticulously measured, the procedure for twins typically takes longer than a singleton scan. You should plan for the appointment to last approximately 30 to 45 minutes.

Caution Before Taking the Test

For your comfort and safety, please inform the sonographer before the test begins if you:

• Have any known allergies, especially to latex.
• Have had recent abdominal surgery.
• Are experiencing any significant pain or discomfort in your abdomen.