Two commonly discussed types of prenatal ultrasound scans are the Target Scan and the Anomaly Scan, each serving distinct purposes in prenatal care. Target Scan assesses early risk of chromosomal abnormalities in weeks 11-14, Where as An Anomaly Scan, also known as a Mid-Pregnancy Scan or Level 2 ultrasound, is performed between weeks 18 to 22 of pregnancy. It assesses the fetus's anatomy to detect structural abnormalities.
Comparative table
Below is the difference between Target Scan and Anamaly Scan in the tabular format for you to understand better.
|
Feature |
Target Scan |
Anomaly Scan |
|
Timing |
Weeks 11-14 |
Weeks 18-22 |
|
Purpose |
Assess risk of chromosomal abnormalities |
Detailed anatomical assessment |
|
Diagnostic Focus |
Nuchal translucency measurement, |
Fetal anatomy including brain, spine, |
|
biochemical markers |
heart, kidneys, limbs, and organs |
|
|
Risk Assessment |
Calculates risk for Down syndrome, |
Identifies structural anomalies that |
|
Trisomy 18, Trisomy 13 |
may affect development |
|
|
Follow-up |
May recommend further testing like CVS, |
Guides management, additional tests |
|
amniocentesis if high risk indicated |
if abnormalities detected |
|
|
Timing of Results |
Early assessment |
Comprehensive evaluation mid-pregnancy |
|
Intended Outcome |
Screening tool |
Detailed diagnostic evaluation |
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What is a Target Scan?
A Target Scan, also known as a First Trimester Screening or Nuchal Translucency (NT) scan, typically occurs between weeks 11 and 14 of pregnancy. This non-invasive procedure involves an ultrasound examination combined with maternal blood tests to evaluate the risk of chromosomal abnormalities such as Down syndrome, Edwards syndrome, and Patau syndrome.
Timing and Purpose
- Timing: Typically performed between weeks 11 and 14 of pregnancy.
- Purpose: The primary goal is to assess the risk of certain chromosomal abnormalities in the fetus, such as Down syndrome (Trisomy 21), Edwards syndrome (Trisomy 18), and Patau syndrome (Trisomy 13).
Procedure
- Ultrasound Examination: A high-frequency ultrasound probe is used to measure the clear space at the back of the fetus's neck, known as the nuchal translucency. This measurement helps in assessing the likelihood of chromosomal abnormalities.
- Maternal Blood Tests: Often combined with biochemical markers obtained from maternal blood samples (e.g., free beta-hCG and PAPP-A levels). The results from these tests, along with the ultrasound findings, contribute to a risk assessment calculation.
Risk Assessment
- Calculation: The scan provides a calculated risk assessment based on the measurements of nuchal translucency and biochemical markers. This assessment helps in categorizing the fetus into low-risk or high-risk categories for chromosomal abnormalities.
- Guidance for Further Testing: Depending on the risk assessment results, healthcare providers may recommend additional diagnostic tests such as chorionic villus sampling (CVS) or amniocentesis to confirm the presence of any genetic conditions.
Safety and Comfort
Safety and comfort are pivotal during Target Scan procedures, prioritizing non-invasiveness and minimal risk to both mother and fetus. This ensures a reassuring experience for expectant parents while facilitating early detection of potential chromosomal abnormalities, contributing to informed decision-making and optimal prenatal care.
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What is an Anomaly Scan?
The anomaly scan, also known as the mid-pregnancy ultrasound scan or the fetal anomaly ultrasound, is typically performed between weeks 18 and 22 of pregnancy. Unlike the NT scan, which focuses primarily on assessing chromosomal abnormalities, the anomaly scan is a more comprehensive examination aimed at detecting structural abnormalities in the developing fetus.
Timing and Purpose
- Typically performed between weeks 18 and 22 of pregnancy, ideally around 20 weeks.
- Also known as the mid-pregnancy ultrasound scan or fetal anomaly ultrasound.
- Aimed at a detailed assessment of fetal anatomy and development to detect structural abnormalities.
Procedure and Imaging
- Typically performed transabdominally using ultrasound gel and a handheld device.
- In some cases, a transvaginal ultrasound may be used for better visualization, especially in early or difficult-to-image pregnancies.
- Takes longer than the NT scan, usually around 30-45 minutes, due to the comprehensive nature of the examination.
Risk assessment
It involves detecting structural abnormalities in fetal anatomy. This comprehensive ultrasound evaluates organs, limbs, and the umbilical cord for any developmental issues. Identification of abnormalities allows for timely intervention or preparation before birth, supporting informed decision-making and optimizing pregnancy management.
Safety and Comfort
- Safe and non-invasive procedure for both the mother and the fetus.
- Painless for the mother, although some discomfort may occur due to the need for a full bladder for optimal imaging.
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Key differences between Target Scan and Anomaly Scan
- Timing: Target Scan (11-14 weeks) screens for chromosomal abnormalities early in pregnancy, while Anomaly Scan (18-22 weeks) assesses fetal anatomy.
- Purpose: Target Scan evaluates risk, guiding further testing. Anomaly Scan provides detailed anatomical assessment, detecting structural abnormalities for management planning.