Everything You Need to Know About the 20-Week Ultrasound

If you’re pregnant, an exciting milestone to look forward to is the 20-week ultrasound.

The 20-week ultrasound scan is the point in your pregnancy when your doctor will be able to give you a much more detailed glimpse into what your baby looks like along with other information.

In this article, we will discuss everything you need to know about the 20-week ultrasound.

We will discuss how an ultrasound works, what is involved in the procedure, and what you can expect to see.

We will also provide some tips so you are prepared for getting through the 20-week ultrasound with ease.

How does an ultrasound work?

Ultrasounds are a non-invasive method that uses sound waves to create an image of objects inside your body.

The technician will put a gel on your stomach and then move a wand over your skin. The wand sends out sound waves, and the echoes are picked up by the wand and turned into an image.

Ultrasound technology is also used in other fields to measure distances and detect objects using the same sound waves.

The sound used for ultrasounds is the same as any sound you hear; however, the sound waves used for ultrasounds are at a higher frequency above the audible limit for the human ear.

There are a few different kinds of ultrasounds that are available to you in terms of image quality and they are 2D, 3D, and 4D.

A standard 2D ultrasound will give you a two-dimensional image of your baby. A three-dimensional ultrasound will give you a more detailed ultrasound image of your baby and a four-dimensional ultrasound gives you a moving, detailed image of your baby.

ultrasound image

What is the 20-week ultrasound?

The 20-week ultrasound is an ultrasound that is performed between weeks 18 and 22 of pregnancy.

It is sometimes called the anatomy scan or 20-week anatomy scan because it is used to examine your unborn baby’s development.

A routine 20-week ultrasound scan is also used to take measurements to ensure the pregnancy is progressing according to plan and that nothing is wrong with your baby.

Your doctor or nurse will take pictures of your baby using ultrasound that you can take home with you too.

What is the purpose of the 20-week ultrasound?

The 20-week ultrasound can be used to determine your baby’s sex, detect major abnormalities, take measurements, and check for problems with the placenta or umbilical cord.

Below we will detail how all of these actions are done during the ultrasound.

Identifying the sex of your baby

Identifying the sex of your baby is one of the most common reasons for having a 20-week ultrasound.

You may want to find out your baby’s sex during this appointment, or you may prefer a surprise on the day of delivery.

The 20-week ultrasound is very accurate in determining the sex of your baby.

The ultrasound tech can usually determine the baby’s sex by looking at the external sex organs, but if they are unsure, they may need to do additional tests such as a scan of the baby’s internal organs.

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Detecting abnormalities

Detecting major abnormalities via prenatal testing is another important purpose of the 20-week scan.

Major abnormalities, including genetic disorders and birth defects, are problems with the baby that can cause death or long-term health problems.

Some of these abnormalities can be detected through ultrasound as early as 11 weeks, but the 20-week ultrasound is considered to be the most accurate for detecting them. The abnormalities that are tested for include:

  • Cleft lip
  • Down syndrome
  • Neural tube defects or defects of the brain, spine, or spinal cord
  • Trisomy 18 which is also called Edwards syndrome
  • Organ abnormalities
  • Congenital heart defect or cardiac abnormalities
  • Chromosomal abnormalities using a level 2 scan

If the ultrasound technician detects any of these abnormalities, they will refer you to a specialist for further evaluation and diagnostic tests.

Measuring the baby

The 20-week ultrasound is also used to measure your baby and information gleaned from this ultrasound is used to calculate the estimated date of delivery (EDD) and track the baby’s growth.

The technician will take measurements of the following fetal anatomy:

  • Face
  • Head
  • Arms
  • Legs
  • Brain
  • Heart
  • Spine
  • Kidneys
  • Stomach
  • Genitals
  • Bladder
  • Diaphragm
  • Hands
  • Feet
  • Chest

Your technician will also listen to your baby’s heartbeat to determine the fetal heart rate and check your amniotic fluid levels to make sure there is enough for your baby.

Checking for problems with the placenta or umbilical cord

Another purpose of the 20-week ultrasound is to check for problems with the placenta or umbilical cord.

The technician will look at the shape and appearance of the placenta and check to see if you are at risk for placenta previa, which is when your placenta covers the opening to your cervix and can cause problems during delivery.

The baby’s umbilical cord is also examined to determine if it is attached to your abdomen and to ensure it has the usual three blood vessels.

How is the 20-week ultrasound performed?

The 20-week ultrasound is a fairly simple procedure that is performed in your doctor’s office.

You will be asked to remove your clothes from the waist down and lie on your back on an exam table.

A gel will be applied to your abdomen and the ultrasound technician will use a wand-like device to scan your baby.

The technician will take pictures and measurements of your baby and will also listen to the baby’s heartbeat. A vaginal ultrasound may also occur where the technician inserts an ultrasound wand in your vagina to check to ensure your cervix is closed. The appointment normally lasts around 45 minutes but plan to be there for over an hour just in case.

You may also meet your doctor after the ultrasound is done to discuss any plans for your pregnancy going forward.

Are there any tips for the 20-week ultrasound?

Here are a few things to keep in mind when you are having your 20-week ultrasound:

  • Try to relax and don’t worry if you can’t see your baby very well as the technician will be taking pictures and measurements of your baby
  • Depending on your baby’s positioning you may need to move around for the technician to get a good image for them to perform their work
  • Do not eat a large meal before your appointment, but you don’t need to fast either
  • If you are having a vaginal ultrasound, you may want to empty your bladder before the appointment
  • If you have any questions or concerns, don’t hesitate to ask your technician or doctor, and do not get discouraged if a technician can not answer your questions due to company policy
  • Do not be afraid to ask for a break if you need one
  • You can bring someone in the room with you for support but do not bring multiple people


The 20-week ultrasound is a routine ultrasound that is performed during pregnancy to detect any abnormalities, measure your baby, and identify the sex of your baby if you would like, and it is also used to check for problems with the placenta or umbilical cord.

The appointment usually lasts around 45 minutes but plan to be there for over an hour to give yourself plenty of time and you can bring someone for support too.

The 20-week ultrasound scan is a great opportunity for you to see your baby and get a sneak peek at what your baby will look like. If you have any more questions or concerns, don’t hesitate to ask your technician or doctor.

References and Sources:

20 week Ultrasound – whattoexpect.com

20 week Scan – nhs.uk