A pregnancy ultrasound is an imaging test that uses high frequency sound waves to create pictures of a baby in the womb, as well as the mother’s reproductive organs. The average number of ultrasounds varies with each pregnancy and should only be used when medically indicated.
An ultrasound, also called a sonogram, can help to monitor normal fetal development and screen for any potential problems. Along with a standard ultrasound, there are a number of different, more advanced, ultrasounds—including a 3D ultrasound, a 4D ultrasound, and a fetal echocardiography, which is an ultrasound that looks in detail at the fetus’ heart.
An ultrasound can be used for a variety of reasons during pregnancy, depending on the stage in which it is done. Your doctor may order more ultrasounds if he or she detected a problem in a previous ultrasound or blood test. Ultrasounds may also be done for non-medical reasons, such as to produce images for the parents or to determine the sex of the baby. While ultrasound technology is safe for both mother and child, healthcare practitioners discourage the use of ultrasounds when there is no medical reason or benefit.
In the first trimester of pregnancy (weeks one to 12), ultrasounds may be done to:
- confirm pregnancy
- check the fetal heartbeat
- determine the gestational age of the baby and estimate a due date
- check for multiple pregnancies
- examine the placenta, uterus, ovaries, and cervix
- diagnose an ectopic pregnancy (when the fetus does not attach to the uterus) or miscarriage
- look for any abnormal growth in the fetus
In the second trimester (12 weeks to 24 weeks) and the third trimester (24 weeks to 40 weeks or birth), an ultrasound may be done to:
- monitor the fetus’ growth and position
- determine the baby’s sex
- confirm multiple pregnancies
- look at the placenta to check for problems, such as placenta previa (when the placenta covers the cervix) and placental abruption (when the placenta separates from the uterus prior to delivery)
- check for characteristics of Down syndrome (normally done between 13 and 14 weeks)
- check for congenital abnormalities or birth defects
- examine the fetus for structural abnormalities or blood flow problems
- monitor the levels of amniotic fluid
- determine if the fetus is getting enough oxygen
- diagnose problems with the ovaries or uterus, such as pregnancy tumors
- measure the length of the cervix
- guide other tests, such as amniocentesis
- confirm an intrauterine death
In order to get a clear image of the fetus and your reproductive organs in the earlier part of the pregnancy, you may need to have a full bladder during your ultrasound. You should drink two to three eight-ounce glasses of water one hour before your scheduled ultrasound. You should not urinate before your ultrasound, so you arrive at your appointment with a full bladder.
To perform a pregnancy ultrasound, you will be instructed to lie down on an examination table or bed. An ultrasound technician will apply a special gel to your abdomen and pelvic area. This gel is water-based, so it should not leave marks on your clothes or skin. This gel helps the sound waves to travel properly.
Next, the technician will place a small wand, called a transducer, onto your belly. The technician will move the transducer to capture black and white images onto the ultrasound screen. He or she may also take measurements of the image on the screen. The technician may ask you to move or to hold your breath while capturing images.
A transvaginal ultrasound may be done to produce a clearer image. This is more likely to be used during the early stages of pregnancy, when capturing a clear image may be more difficult. For this test, a small ultrasound probe will be inserted into the vagina. The probe will rest against the back of your vagina while the images are captured.
The technician will check to see if the necessary images have been captured and are clear. The gel will then be wiped off and you will be able to empty your bladder.
Other, more advanced ultrasound techniques may be used when a more detailed image is required. This may be done to provide the doctor with the necessary information to make a diagnosis if problems were detected during your traditional ultrasound.
Unlike a traditional 2D ultrasound, a 3D ultrasound allows your doctor to see the width, height, and depth of the fetus and your organs. This can be especially helpful in diagnosing any suspected problems during your pregnancy.
A 3D ultrasound follows the same procedure as a standard ultrasound, but uses a special probe and software to create the 3D image. It also requires special training for the technician, so it may not be as widely available.
A 4D ultrasound may also be called a dynamic 3D ultrasound. Unlike other ultrasounds, a 4D ultrasound creates a moving video of the fetus. This creates a better image of the baby’s face and movements. A 4D ultrasound is also better able to capture highlights and shadows. A 4D ultrasound is done in a similar manner to other ultrasounds, but with special equipment.
A fetal echocardiography is performed if your doctor suspects your baby may have congenital heart defects. This ultrasound captures an in-depth image of the fetus’ heart—one that shows the heart’s size, shape, and structure.
This ultrasound also gives your doctor a look at how your baby’s heart is functioning, which can be helpful in diagnosing heart problems. This test may be done in a similar manner to a traditional pregnancy ultrasound, but might take longer to complete.