What is a pregnancy ultrasound?
A pregnancy ultrasound is a test that uses high-frequency sound waves to image the developing baby as well as the mother’s reproductive organs. The average number of ultrasounds varies with each pregnancy.
An ultrasound, also called a sonogram, can help monitor normal fetal development and screen for any potential problems. Along with a standard ultrasound, there are a number of more advanced ultrasounds — including a 3-D ultrasound, a 4-D ultrasound, and a fetal echocardiography, which is an ultrasound that looks in detail at the fetus’ heart.
During the first trimester of pregnancy
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
During the second and third trimesters of pregnancy
In the second trimester (12 to 24 weeks) and the third trimester (24 to 40 weeks or birth), an ultrasound may be done to:
- monitor the fetus’ growth and position (breech, transverse, cephalic, or optimal)
- 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
A transvaginal ultrasound may be done to produce a clearer image. This ultrasound 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 is inserted into the vagina. The probe rests against the back of your vagina while the images are captured.
Unlike a traditional 2-D ultrasound, a 3-D ultrasound allows your doctor to see the width, height, and depth of the fetus and your organs. This ultrasound can be especially helpful in diagnosing any suspected problems during your pregnancy. A 3-D ultrasound follows the same procedure as a standard ultrasound, but it uses a special probe and software to create the 3-D image. It also requires special training for the technician, so it may not be as widely available.
A 4-D ultrasound may also be called a dynamic 3-D ultrasound. Unlike other ultrasounds, a 4-D ultrasound creates a moving video of the fetus. It creates a better image of the baby’s face and movements. It also captures highlights and shadows better. This ultrasound is performed similarly to other ultrasounds, but with special equipment.
A fetal echocardiography is performed if your doctor suspects your baby may have congenital heart defects. This test may be done similarly to a traditional pregnancy ultrasound, but it might take longer to complete. It 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.