Most pregnant women have an ultrasound at around 20 weeks.

Doctors call this an anatomy or morphology scan. It reveals a lot about the fetus’s health and development. It can also indicate certain health risks to the woman and help inform decisions about the delivery.

In this article, we explore this scan in detail, including what to expect at the appointment.

During pregnancy, an ultrasound provides a way to see the fetus, the uterus, and some other relevant structures, using sound waves.

A doctor or an ultrasound technician may perform the scan. They use a handheld device called a transducer to send the sound waves into the abdomen. The waves then bounce off the fetus and surrounding structures, and the returning waves form an image, which is visible on a monitor.

The image is not a photo, and it may not be very detailed. The goal is to provide basic but essential information about the fetus’s shape, development, and overall health.


The woman lies on an exam table, and the doctor or technician squeezes gel onto the woman’s bare abdomen. They then move the transducer around the area and check the returning images on the monitor.

For some parts of the ultrasound, the woman may need to have a full bladder, which can make the pictures clearer. If this happens, the healthcare provider will perform these parts of the scan first, then take a break so that the woman can use the bathroom.

A healthcare provider may also recommend a vaginal ultrasound to provide a better image. This involves inserting a thin transducer into the vagina, and it requires the woman to undress from the waist down.

If a technician performs the ultrasound, they may not share what they find during the scan. In this case, a doctor will meet with the woman shortly afterward to discuss the results. This does not necessarily indicate that anything is wrong.


Ultrasounds are safe; there is no evidence that they harm the fetus.

However, The American College of Obstetricians and Gynecologists caution that because we cannot know everything about the possible effects, a woman should only have this type of scan when it is medically necessary.

The Food and Drug Administration (FDA) also warn that nonmedical, or keepsake, ultrasounds may not be safe. They are often performed in nonclinical settings.

During a traditional 20-week ultrasound, the doctor or technician checks the fetus’s major organs and systems. The goal is to ensure that the heart, brain, skull, kidneys, bones, hands, and feet are developing as usual and that the fetus is the right size for its stage of development.

Also, they can check on the:

  • Number of fetuses: Most women know whether they are having twins, for example, by 20 weeks, but if this is the first ultrasound of the pregnancy, the technician or doctor checks.
  • Sex: If a woman has not already had bloodwork to find out the sex of the fetus, they can often find out at the 20-week ultrasound, depending on the fetus’s position.
  • Health of the pregnancy: Using the scans, a doctor can determine the location of the placenta, assess amniotic fluid levels, and generally check that the pregnancy is progressing as usual. The findings can also help inform the plan for the delivery.
  • Fetal heart rate: It is usually possible to hear the fetus’s heart during this ultrasound, which can provide valuable information. At 20 weeks, a healthy heart rate is around 140 beats per minute.

These ultrasounds show the fetus in more detail.

3D ultrasounds send sound waves from many angles and use them to create a composite image. 4D ultrasounds work similarly but also allow viewers to see detailed movement.

Compared with the traditional 2D scan, a 3D or 4D can show more body parts, fine details of the fetus’s face and its expression, as well as movement, such as thumb-sucking.

Sometimes, a doctor requests a 3D or 4D ultrasound if they cannot see certain areas clearly in 2D or if they suspect a complication.

In most cases, though, there is no medical reason for 3D or 4D scans.

The 20-week ultrasound provides a lot of information about a developing fetus and the health of the pregnancy.

It is not a perfect diagnostic tool, however. It cannot detect all congenital disabilities, and sometimes it gives misleading information. A doctor may not be able to see all body parts or they may recognize an issue that, on a later scan, turns out to be nothing.

It is important to understand the full purpose of the scan and to ask questions. If any questions remain, or if the scan reveals potential problems, a follow-up appointment may be necessary.