How to Read Ultrasound Numbers

Ultrasound, also known as a sonogram, is a method of imaging that uses a high amount of frequency in sound waves, thus producing images of a certain part of your body.

Physicians focus on capturing ultrasonic images of the uterus and the growing baby inside it for pregnancy ultrasound. 

On the other hand, ultrasound numbers are a part of ultrasound imaging. 

They’re found on the topmost part and contain details of the patient. In this article, you will be able to learn and understand how to read ultrasound numbers.

So, let’s find out about the ultrasound numbers. 

How to Read Ultrasound Numbers

While many physicians don’t explain to patients what the numbers on the ultrasound results mean, this is still a vital topic to discuss when dealing with a pregnancy ultrasound.

To start, you should know that the topmost part of a sonogram picture contains information about a patient. 

Meanwhile, the number found under the name in a pregnancy ultrasound is gestation age. 

Next to it is the date and time the ultrasound was taken, also found below the name of the diagnostics clinic.

The numbers on the upper right part with letters beside them have corresponding significance to the ultrasound results. 

Some of these are the TiS (Thermal Index for Soft Tissues), TiB (Thermal Index in Bones), and Mi (Mechanical Index).

You can also see numbers and letters on the right part of the ultrasound image. 

These are CRL (Crown-rump Length), BPD (Biparietal Diameter), Fe (First Trimester Embryo), FL (Femur Length), UV (Umbilical Vein), st (Stomach), and sp (Transverse Spine).

This is just an overview of what ultrasound numbers on an image are.

When physicians explain an ultrasound image, they don’t usually tackle these parts or explain how to read ultrasound numbers. 

This is mostly because it’s no longer important to specifically discuss what the ultrasound numbers are and discuss the image itself directly.

Explaining the Ultrasound Numbers

You can also see ultrasound numbers when obtaining a fetal image, aside from the image itself.

Here’s a brief explanation of how to read ultrasound numbers and what they mean:

Crown-Rump Length

This is the accurate gestational age predictor. It has been said to be the most precise way of getting the dates of a pregnancy.

There is a programmed table to explain a crown-rump length and how to compute it. 

For example, approximately adding the fetal CRL in centimeters and 6.5 gives the gestation age in weeks.

The CRL is an important ultrasound number because you can know the age of the pregnancy through this and be able to start the monitoring from there.

Biparietal Diameter

While CRL is necessary to know the exact age of gestation. However, it is no longer wise to use that method after the first trimester because of the fetal position and size.

This is why BPD or Biparietal Diameter is used during this time.

The BPD is the largest transverse method to measure the fetal skull. When calculating the BPD, you would come across these abbreviations:

  • OF (Occipitofrontal) 

This is to measure the BPD.

  • SB (Suboccipitobregmatic)

This shows the anatomy of the posterior fossa.

First Trimester Embryo

The most crucial part of every pregnancy is mostly the first trimester. This is one of the reasons it’s necessary to do an ultrasound during this time to see the development of the fetus, particularly the femur length. 

The Fe or first-trimester embryo is the process of checking the embryo’s size during the first part of the pregnancy. This is done by measuring from the head or the crown to the buttocks or rump of the fetus. 

Umbilical Vein, Stomach, and Transverse Spine

All of these are measured in an Abdominal Circumference or known as the Mean Abdominal Diameter. To measure this, a transverse plane is needed. This is positioned perpendicular to the fetal spine, the stomach level, and the umbilical vein.

The formula to compute the Abdominal Circumference in ultrasound numbers is multiplying the mean abdominal diameter by π or 3.14. Another way is by using the perimeter system found on the ultrasound image. 

Assess the Age of Gestation

Gestational age and ultrasound numbers are very related because what we see in the ultrasound images depicts the age of the fetus. 

Then, the data are compared with the dimensions to obtain a conception date.

To better understand this, you can check out this table, which shows the fetal growth parameters.

See a related post: What Is The Best Time For 4D Ultrasound Scan?


In general, ultrasound numbers aren’t discussed with patients when they get an ultrasound image.

Yet, it’s still considered critical for them to know that the numbers and abbreviations are in the pictures. 

That’s because learning how to read ultrasound numbers allows them to understand better how the data has been gathered and explain more clearly how the fetus grows inside a mother’s belly.

Moreover, these ultrasound numbers help them understand the process and results of the obstetric ultrasound.

This significantly helps them with making decisions when a situation calls for it.

That’s why it’s imperative that physicians do not leave the ultrasound numbers undiscussed.

Frequently Asked Questions

Can ultrasound numbers determine fetal abnormalities?

Yes, since they show the size of the fetus and how it is growing inside. In this case, any fetal abnormalities are detected through the measurements of the ultrasound numbers.

How are ultrasound numbers accurate in giving the results?

Ultrasound imaging is not 100% accurate. However, you should note that the way it gives the exact measurements of the fetus can already be a good start for determining fetal abnormalities.

In this case, physicians can detect the anomalies and request additional tests to confirm them through this.

Is ultrasound safe for the baby?

Yes. It is a painless and non-invasive way to see the uterus from the inside.

That’s because instead of using radiation, it uses sound waves to get a picture of the fetus.

In fact, no dangerous risks have ever been established in sonography over the years.

Physicians are also the ones who conduct the ultrasound, making sure that no harm is done during the entire process and that everything is safe.



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