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20 Week Ultrasound

The 20 week scan is the second routine ultrasound offered by your hospital. This will often be the second time you get to see your baby, unless you have paid for private scans or been referred for more scans by your doctor due to bleeding or abdominal pain. This scan is often called the anatomy or gender scan, but it is used to check your baby’s anatomy and that they’re developing properly as well as the gender.

The 20 week ultrasound is often longer than the 13 week scan because the sonographer will have more measurements to take. These can indicate genetic conditions as well as ailments like spina bifida, congenital heart abnormalities, and limb differences.

How do 20 week ultrasounds work?

The 20 week ultrasound is the exact same as your 13 week scan, using a probe and water-based gel on your stomach to project images onto a computer screen, allowing you to see real-time video footage of your baby.

The probe turns electrical currents into sound waves that penetrate your skin and travel deeper into your stomach until they hit something. Once they find something, the sound waves bounce off the object and travel back to the probe. The probe then converts them back into electrical currents, which can be sent to the attached computer.

The computer detects patterns in the electrical currents to project an image of your baby on the screen. This all happens within seconds so you can see your baby moving in real time, and your sonographer can take more accurate measurements. Generally, ultrasounds and sound waves are not harmful to you or your baby.

Why might you need a 20 week ultrasound?

The 20 week scan is one of the routinely offered ultrasounds for parents as it’s used as a risk assessment for you and your baby. It’s important that you attend the appointment as they can provide information that might mean you need to make further important decisions in regard to your baby. The scan keeps you and your doctor in the know so you both know the condition and development of your baby.

There are multiple reasons why you should have your 20 week ultrasound, including:

  • To confirm your baby is developing correctly and they look to be the correct size
  • To make sure there are no concerns surrounding the baby’s bones, brain, heart, spinal cord, face, kidneys, and abdomen
  • To check on the placenta and its size, as well as where it’s lying in relation to your baby
  • To locate the umbilical cord and whether it’s in a compromising position
  • To measure the amount of fluid around your baby

The sonographer can also look for 11 rare conditions at the anatomy scan. While the scan looks for these conditions, there is no guarantee that it will be able to find everything that might be concerning. The sonographer will look for the following rare conditions:

  • Anencephaly
  • Open spina bifida
  • Cleft lip
  • Diaphragmatic hernia
  • Gastroschisis
  • Exomphalos
  • Serious cardiac abnormalities
  • Bilateral renal agenesis
  • Lethal skeletal dysplasia
  • Edwards’ syndrome (T18)
  • Patau’s syndrome (T13)

How to prepare for your 20 week ultrasound

The 20 week scan appointment letter will tell you everything you need to do to prepare for your scan, as most hospitals have their own policies about this. Most ultrasound scans won’t need much preparation, but it’s worth checking with your doctor if you’re unsure.

Most hospitals will ask you to drink a litre of water before your appointment so that your bladder is full for the scan. This helps your sonographer see the baby more easily and take more measurements. Depending on the size and position of your baby, they might ask you to empty your bladder halfway through the appointment.

Your sonographer will need to take plenty of measurements at this scan and see your baby from different angles. They might ask you to bring a sugary drink or snack to help get your baby more active or ask you to walk around to reposition them between scans.

Most hospitals allow you to bring a support person with you but avoid bringing children. This appointment is long and quiet, and your ultrasound technician will need peace to focus on all the measurements.

As the anatomy scan tends to be longer than most other ultrasounds, it’s advised that you wear comfortable clothing as you’ll be lying down for a while. Loose clothing will also help your sonographer get better access to your stomach throughout the scan.

What to expect from your 20 week ultrasound

During the scan

20 week scans are offered through a transabdominal approach and carried out by a trained sonographer. The scan will be done in a dimly lit room so the sound waves can pick up better images of your baby.

When entering the sonography room, you’ll be asked to lie on the cushioned table and pull your waistband down slightly. Depending on where your baby is lying, you might also have to lift your top slightly. Your support person will be able to sit next to you.

The sonographer will then tuck a paper towel into your waistband to protect your clothing from getting covered in gel. The gel is water-based and will be squirted onto your stomach when the scan is ready to begin. This will allow the probe to keep a better connection with your skin to help the sound waves pass through your body.

Your sonographer will then pass the probe over your baby’s body to examine them. A 2D picture of them will be seen on the screen then, and you’ll often be able to take a look at your baby.

The scan will be quite quiet while your ultrasound technician is taking measurements and pictures. They’ll have a long checklist to work through, so they might not talk to you much throughout the appointment.

Sonographers aim to get every measurement done in one scan, but sometimes this is not possible. If your baby is sleeping or tired, they might not want to move in the best position to get all of the measurements. Your sonographer might ask you to move your hips or walk around to help move the baby. You might also be offered a sugary drink to get them moving.

If this still doesn’t work, you might be asked to come back in a few hours to finish the ultrasound when the baby is more alert and responsive.

Most 20 week ultrasounds take around 30 minutes, but some might take longer if your baby is in an unfavourable position. Some hospitals ask you to allow for 60 minutes for the anatomy scan.


After the scan

After the scan has finished and the sonographer has all the measurements and results they need, you’ll be able to wipe the gel from your stomach and readjust your clothing. Your sonographer might ask if you want to know your baby’s sex, and they’ll tell you if you say you want to know. You can opt for no, too.

Your results will then be sent to your doctor who will review them in detail and answer any questions you have about the scan and your baby.

The anatomy scan is a great indication of how your baby is growing and ready for birth. The results of this scan will help your doctor tailor the rest of your treatment plan to make sure you and your baby are cared for.

Once you and your doctor are happy with your results, you can resume everyday activities like normal.

What are the benefits of 20 week ultrasounds?

The 20 week pregnancy scan is performed to make sure your baby is growing at the correct rate and that there are no abnormalities to be concerned with that need more tests. While the anatomy scan cannot rule out every concern, it goes a long way in putting parents’ minds at ease.

  • The anatomy scan looks at every part of your baby’s body to make sure they are growing at the correct rate and are not too large or small

  • The scan will be able to identify the sex of your baby if you want to know

  • The 20 week scan can spot 11 rare conditions so your doctor can update your treatment plan should any concerns arise

  • The anatomy scan might be able to inform your doctor of any changes to the rest of your pregnancy plan to keep you and your baby safe


What usually happens at a 20-week scan?

The 20 week ultrasound is often the longest scan of your pregnancy as your sonographer will have a long list of measurements to take. You will be able to see your baby throughout the scan and you’ll see different parts of their body, including their legs, hands, face, spine, and more. You will often be asked if you want to know the sex of the baby. The sonographer will generally be quite quiet during the appointment and questions can be answered by the doctor after your scan has concluded.

Does the 20 week scan show gender?

At 20 weeks, a gender scan is generally considered accurate and therefore your sonographer should be able to tell you the sex of your baby. However, some hospitals might have policies that dispute this, so it’s all down to your hospital and sonographer. Mention at the start of the appointment if you want to know the sex or not.