What to expect at an ultrasound

feb 11, 2022 | 3 minutes Leer

Even if you have never personally had one, you probably have heard of pregnancy ultrasounds. Pregnancy ultrasounds are just one of the many screening tools available to assess that all is going well with a mother's pregnancy and the growth and development of her baby. Most women will have at least one pregnancy ultrasound, either in very early stages of their pregnancy or at around 20 weeks of gestation.

Other names for pregnancy ultrasounds are a pregnancy dating scan, which is commonly done within the first trimester, and a pregnancy anomaly or screening ultrasound. The pregnancy anomaly or screening ultrasound is commonly done at around 18-20 weeks of gestation. If the maternity care provider is concerned about the baby's growth in the third trimester, then an additional ultrasound at this stage may be recommended. Determining the baby's size, weight, and growth as well as the amount of amniotic fluid present can provide a comprehensive assessment of the baby's status.

Sometimes during a third trimester ultrasound, findings reveal that the baby would be safer in a neonatal intensive care unit (NICU) than to remain in the uterus. In these cases, the risks associated with prematurity are not considered to be as significant to the baby's health as the risks if the pregnancy continues.

What is a pregnancy ultrasound?

A pregnancy ultrasound is a scan where an ultrasound machine sends high-frequency sound waves through a mother's uterus or her vagina. These sound waves are higher than can be registered by the human ear, which is why pregnancy ultrasound is a quiet procedure. The sound waves are emitted from a small, vibrating crystal housed in a handheld device known as a transducer. It is a painless procedure and will not hurt you or your baby.

During a pregnancy ultrasound, the sound waves created bounce off the baby and in turn are interpreted into an image on a screen. These images are occurring in real time; there is no delay between when the images are picked up and when they can be seen on the screen. You can see your baby moving around and kicking in real-time, rather than snapshots of still imagery.

Warm, translucent gel is first applied to the mother's abdomen. This helps to reduce the traction between the transducer and the skin and assists in transmitting the ultrasound waves with less interference so they can pass from the transducer through mother's body.

On the ultrasound, hard tissues such as bone appear white, and soft tissues appear grey. Amniotic fluid appears black. Each shade and its intensity are interpreted by a sonographer and provide different information.

What you’ll see at an ultrasound

You will be able to see a lot of your baby, in terms of their physical shape and appearance. You’ll see all their internal organs including their brain, heart, lungs, kidneys, liver and stomach. You will also see their spine, their limbs, their genitals, and their movements.

You will be given a photograph of one or two of the ultrasound images to take home with you. Some practices offer video; some do not. Speak with the individual sonography service to see what they offer.

How an ultrasound works

Pregnancy ultrasound has been done routinely for the last forty years. There have been multiple research studies conducted over the years looking at the potential risks to mothers and their babies, but to date there is no consistent evidence that ultrasound is unsafe for either.

Pregnancy ultrasounds are also noninvasive, which means that it will be done through the skin on your abdomen or vaginally. An ultrasound is not a surgical procedure; there is no cutting into or around the skin. An ultrasound does not use radiation like an X-ray would, so it is considered much safer to use as a diagnostic tool during pregnancy.

Currently, the sonography industry is well-monitored and regulated and the staff training very comprehensive.

Why you need a pregnancy ultrasound

There are many reasons for having a pregnancy ultrasound, but some of the most common are:

  • To diagnose a viable pregnancy.
  • To assess the gestational age of the baby.
  • To check the baby's growth and development.
  • To check how many babies are present in the mother's uterus.
  • To see where the placenta is positioned.
  • To do a nuchal fold measurement at the back of the baby's neck and to assess if there is an increased risk of the baby having Down Syndrome. This specific measurement needs to be conducted between 11 to 14 weeks.
  • To assess for specific problems the baby may have, such as spina bifida.
  • To assess the baby's gender; though this is not a primary reason for pregnancy ultrasound, it is often determined at the 20-week screening scan.
  • To assess the cause of pregnancy complications. This may be bleeding, a decrease in the baby's movements or if the mother has been experiencing pain.
  • To detect whether there is an ectopic pregnancy. This is when the baby is growing outside of the mother's uterus, most commonly in one of the fallopian tubes.
  • When an amniocentesis or chorion villus sampling test is being conducted, a pregnancy ultrasound is done at the same time. This is to ensure that the needle is inserted into the correct area and there is no risk to the baby.
  • To check for uterine fibroids or ovarian cysts.

Where a pregnancy ultrasound takes place

Most large cities have maternal fetal medicine practices associated with health systems which provide pregnancy ultrasounds. You may be referred to one of these, or alternately to your local maternity hospital’s radiology department, or a pregnancy-specific women's health sonography service.

The procedure generally takes around thirty minutes. If you have been scheduled for a vaginal ultrasound and then need to have an abdominal scan, you may be there for up to one hour. Try not to rush. You will want to enjoy your pregnancy ultrasound as much as possible and if you are stressed and anxious, you won’t get everything out of it that you otherwise could.

Your pregnancy ultrasound results

As the sonographer is doing the procedure, they may turn the screen around at some stage and point out various images on the screen. You may also go to a clinic which provides a separate screen to the one the sonographer needs, specifically for parents to look at.

If any concerns arise during the ultrasound, the sonographer will request a second opinion from a colleague. Sometimes this can’t happen at the same time, which means there may be an unavoidable wait. Of course, this can be very worrying for parents, but many times, there is simply a variation of normal which just needs to be clarified.

The results of the scan will be sent to the referring health professional who recommended the scan, and you will be informed of the results. Of course, complications can be detected during ultrasound which is one of the reasons why it is done in the first place. In this case you will be encouraged to speak with your maternity care provider who will be informed by the radiographer's assessment.


Pregnancy ultrasounds are usually done by sonographers who have specialized training in obstetric sonography. They have qualifications in medical ultrasound and have been trained in the procedures, risks, and interpretation of sonography.

How to prepare for a pregnancy ultrasound

If you are having a first trimester ultrasound, then you will need to have a full bladder. Follow the instructions of the ultrasound clinic you are attending. Some recommend that you drink 16 ounces of water in the hour or so preceding the ultrasound and to try not to empty the bladder until after the procedure is done. A full bladder helps to lift the uterus up out of the mother's pelvis so the baby can be seen more clearly.

For the second trimester ultrasound, the general recommendation is the same. For both scans, it is important to take any typical medication that has been prescribed by a provider.

Although a pregnancy ultrasounds are completely painless, sometimes there can be a level of discomfort associated with a full bladder. This can be uncomfortable as the sonographer presses the transducer over the region of the bladder or into the vagina, but it is generally for only a short period of time.

If you cannot tolerate this, tell the sonographer. You might be able to partially empty your bladder or they will find an alternative area in which to place the transducer. Generally, women are advised to empty their bladder before having a vaginal ultrasound. You may also be asked to hold your breath for a short time during the ultrasound. This can happen if the sonographer wants to see a certain image more clearly or needs to take a photo. The simple process of inhaling and exhaling can be enough to affect the focus and clarity of an image, so staying still for moment of time can be useful.

Ultrasounds and gender

It’s likely that you can know the baby’s gender at the 20 week scan—if you want to, and if your baby is cooperating. Sometimes the baby is lying in an awkward position or has its legs crossed, which might make it hard to see the genitals. If you want to keep the baby's sex a secret, then tell the sonographer before the procedure begins.

Remember that the purpose of a pregnancy ultrasound is rarely to soley determine if the baby is a boy or a girl. Rather, it is a medical procedure which is a scientific tool, designed to visualize your baby and the uterus and diagnose if there are any complications. Finding out the gender is just an added bonus!

Vaginal ultrasounds

A vaginal ultrasound is when a transducer is inserted into the vagina to pick up images via the mother's pelvis rather than through the abdominal wall. If you are very early on in your pregnancy or are particularly overweight, doing an abdominal ultrasound may not provide sufficient clarity of the images, and you might be asked to have a vaginal ultrasound instead.

A vaginal ultrasound is not painful and will not harm you or your baby. It is just another option. Vaginal ultrasounds are generally only performed up until 12 weeks of gestation and can be common for the 7 week ultrasound.

A disclaimer on ultrasounds

Ultrasounds are not an exact science. Not all abnormalities can be detected. Problems can be misinterpreted, and mistakes made. Whether these are due to machine, technology or human error is not always clear.

The information of this article has been reviewed by nursing experts of the Association of Women’s Health, Obstetric, & Neonatal Nurses (AWHONN). The content should not substitute medical advice from your personal healthcare provider. Please consult your healthcare provider for recommendations/diagnosis or treatment. For more advice from AWHONN nurses, visit Healthy Mom&Baby at health4mom.org.