A–Z Guide to Prenatal Ultrasound Medical Abbreviations

Every time expectant parents receive an ultrasound report, they are often confronted with a long list of unfamiliar abbreviations such as BPD, FL, CRL, NT, and AFI. To support families throughout pregnancy, TD TECH has compiled the “A–Z Obstetric Ultrasound Dictionary”—a comprehensive and easy-to-understand guide to today’s most commonly used obstetric ultrasound terms.

Fetal Growth and Measurement Parameters

These are the most common measurements found on every prenatal ultrasound report, helping physicians monitor fetal growth and development.

• AC (Abdominal Circumference): Measures the circumference of the fetal abdomen. It is an important parameter for assessing fetal growth and estimating fetal weight during the later stages of pregnancy.
• BPD (Biparietal Diameter): Measures the widest transverse diameter of the fetal head. It is commonly used to determine gestational age and evaluate brain development.
• CRL (Crown–Rump Length): Measures the distance from the top of the fetal head to the buttocks. It is typically measured during the first trimester (7–13 weeks) and provides the most accurate estimate of gestational age.
• FL (Femur Length): Measures the length of the fetal thigh bone. This parameter helps evaluate skeletal growth and may assist in identifying certain skeletal abnormalities or growth restrictions.
• HC (Head Circumference): Measures the circumference of the fetal head. Together with BPD, it is used to assess skull and brain growth.
• EFW (Estimated Fetal Weight): An estimated fetal weight automatically calculated by the ultrasound system using measurements such as BPD, AC, and FL.

Screening Parameters and Pregnancy Environment

These parameters help screen for congenital abnormalities and assess the fetal environment inside the uterus.

• AFI (Amniotic Fluid Index): Measures the amount of amniotic fluid to determine whether it is within the normal range, too low (oligohydramnios), or too high (polyhydramnios).
• EDD (Estimated Due Date): The expected delivery date, calculated based on the first day of the last menstrual period or first-trimester CRL measurement.
• GA (Gestational Age): The duration of pregnancy expressed in weeks and days (e.g., 12W3D = 12 weeks and 3 days).
• NT (Nuchal Translucency): Measures the fluid-filled space at the back of the fetal neck between 11 weeks and 13 weeks + 6 days of pregnancy. Increased NT thickness may indicate an elevated risk of chromosomal abnormalities such as Down syndrome.
• Placenta Grade: Evaluates placental maturity by assessing the degree of placental calcification, typically graded from 0 to III according to gestational age.

Advanced Ultrasound Imaging Technologies

In addition to measurement parameters, ultrasound reports may also include terms describing advanced imaging technologies.

• Color Doppler: Evaluates blood flow to assess fetal circulation through the umbilical cord and uterine arteries.
• 3D/4D/5D Ultrasound: Advanced imaging technologies that reconstruct three-dimensional static images and real-time four-dimensional videos, allowing detailed visualization of the baby’s facial features and movements.
• STIC (Spatio-Temporal Image Correlation): An advanced imaging technology that captures and reconstructs the moving fetal heart in space and time, enabling detailed evaluation of cardiac anatomy.

What Determines the Accuracy of Ultrasound Measurements?

Accurate interpretation of the parameters in this “A–Z Obstetric Ultrasound Dictionary” depends not only on the expertise of the sonographer but also on the quality of the ultrasound system. Poor image quality or excessive noise can lead to inaccurate measurements and unnecessary anxiety for expectant parents.

Premium ultrasound systems such as the Voluson Expert 22 and Voluson Expert 20 are equipped with intelligent SonoBiometry technology. Artificial intelligence automatically identifies the correct anatomical plane and measures key biometric parameters—including BPD, HC, AC, and FL—with a single click, reducing operator-dependent variability while shortening examination time. In addition, SonoCNS automatically aligns standard imaging planes for comprehensive fetal brain assessment.

For small and medium-sized obstetric clinics, the Voluson P8 from TD TECH is an excellent choice. Featuring an intuitive user interface, high-quality 2D/3D imaging, and essential automated biometric measurement tools, it enables healthcare professionals to perform accurate and efficient ultrasound examinations.

Voluson Expert 22 Women’s Health Ultrasound System

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Voluson Expert 20 OB/GYN Ultrasound System

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Voluson P8 OB/GYN Ultrasound System

Voluson Ultrasound System

What Should You Do If an Ultrasound Parameter Is Abnormal?

If one of your ultrasound measurements falls outside the reference range—such as a short FL, increased NT, or low AFI—there is no need to panic. An isolated abnormal value alone is not sufficient to diagnose a fetal condition. The most important step is to consult your obstetrician for a comprehensive evaluation, combining ultrasound findings with appropriate prenatal screening tests and following the recommended schedule for repeat examinations to monitor your baby’s development throughout pregnancy.

We hope this “A–Z Obstetric Ultrasound Dictionary” helps expectant parents better understand their ultrasound reports and feel more confident throughout their pregnancy journey.