NT Scan (Nuchal Translucency Scan)

An NT scan (Nuchal Translucency scan) is a specialized ultrasound performed in the first trimester, typically between 11 and 14 weeks of pregnancy. It measures the thickness of the fluid-filled space at the back of the fetus’s neck, known as the nuchal translucency.

Purpose

• Screening for Chromosomal Abnormalities: The NT scan is a key part of early prenatal screening for genetic conditions such as Down syndrome (trisomy 21), Edwards syndrome (trisomy 18), and Patau syndrome (trisomy 13).
• Detection of Heart Defects: An increased NT measurement may also indicate a higher risk of congenital heart defects or other structural anomalies.
• Combined Screening: The NT scan is often combined with a maternal blood test to improve accuracy in estimating the risk of chromosomal abnormalities.

How the NT Scan is Performed

• Preparation: Usually performed transabdominally, but may be done transvaginally for clearer images.
• Ultrasound Procedure: A gel is applied to the abdomen, and the ultrasound probe is used to visualize the fetus.
• Measurement: The sonographer measures the thickness of the nuchal translucency, which appears as a dark space at the back of the baby’s neck.
• Timing: The scan is most accurate between 11 weeks + 3 days and 13 weeks + 6 days of gestation.

Interpretation of Results

• Normal Range: NT measurements typically range from 1.3 to 2.7 mm. An NT measurement of 3.5 mm or more is considered increased and may indicate a higher risk for chromosomal or structural abnormalities.
• Screening, Not Diagnosis: The NT scan is a screening test, not a diagnostic test. A higher measurement suggests increased risk but does not confirm a diagnosis.
• Next Steps: If the NT measurement is increased, further diagnostic tests such as Non-Invasive Prenatal Testing (NIPT), chorionic villus sampling (CVS), or amniocentesis may be recommended.

Additional Information

• Optional Test: The NT scan is optional and should be discussed with your healthcare provider.
• Other Uses: The scan can also help confirm gestational age, detect multiple pregnancies (twins, etc.), and assess basic fetal anatomy.

Anomaly Scan (Anatomy Scan / 20-Week Ultrasound)

An anomaly scan—also called the anatomy scan or 20-week ultrasound—is a detailed prenatal ultrasound performed between 18 and 22 weeks of pregnancy. Its primary purpose is to systematically examine the fetal anatomy, detect structural abnormalities, and assess fetal growth, placental position, and amniotic fluid volume.

What Does the Anomaly Scan Check?

• Brain and Spine: Detects neural tube defects and brain malformations.
• Face: Checks for cleft lip, palate, and other facial anomalies.
• Heart: Assesses heart chambers and vessels for congenital heart defects.
• Abdomen: Examines the stomach, kidneys, bladder, and bowel for anomalies.
• Limbs: Ensures proper development of arms, legs, hands, and feet.
• Placenta and Amniotic Fluid: Evaluates placental position (e.g., placenta previa), structure, and amniotic fluid volume.
• Maternal Pelvic Organs: Assesses uterus, cervix, and ovaries for abnormalities.

Conditions Identified

Fetal Conditions	Placental Conditions	Maternal Conditions
Anencephaly, spina bifida, cleft lip, congenital heart defect, diaphragmatic hernia, omphalocele, renal agenesis, skeletal dysplasias, Edwards/Patau syndromes	Placenta previa, vasa previa, placenta accreta, velamentous cord insertion	Uterine anomalies, fibroids, short cervix

Importance

• Early Detection: Identifies major structural abnormalities and congenital malformations, some of which may require intervention after birth or influence delivery planning.
• Growth Monitoring: Measures fetal size to monitor growth patterns and detect growth restriction.
• Placental Assessment: Helps plan delivery if placental problems (e.g., placenta previa) are detected.
• Pregnancy Management: Guides further testing, counseling, and management if abnormalities are found.

Limitations

• Not All Anomalies Detected: Sensitivity varies; some conditions may be missed due to fetal position, maternal obesity, or the nature of the anomaly.
• Cannot Detect Functional or Genetic Disorders: Conditions like cerebral palsy or autism cannot be diagnosed by this scan.
• Sex Determination: Fetal sex can often be seen, but sex determination for non-medical reasons is prohibited in many countries, including India.

Safety

• Non-invasive and Safe: Uses sound waves, not radiation, and is considered safe for both mother and fetus.