What is an ultrasound?
An ultrasound scan is a diagnostic technique which uses high-frequency sound waves to create an image of the internal organs. A screening ultrasound is sometimes done during the course of a pregnancy to check normal fetal growth and verify the due date. Ultrasounds may be performed at various times throughout pregnancy for different reasons:
In the first trimester:
- to establish the dates of a pregnancy
- to determine the number of fetuses and identify placental structures
- to diagnose an ectopic pregnancy or miscarriage
- to examine the uterus and other pelvic anatomy
- in some cases to detect fetal abnormalities
Mid-trimester: (sometimes called the 18 to 20 week scan)
- to confirm pregnancy dates
- to determine the number of fetuses and examine the placental structures
- to examine the fetal anatomy for presence of abnormalities
- to check the amount of amniotic fluid
- to assist in prenatal tests such as an amniocentesis
- to examine blood flow patterns
- to observe fetal behavior and activity
- to examine the placenta
- to measure the length of the cervix
- to monitor fetal growth
Third trimester:
- to monitor fetal growth
- to check the amount of amniotic fluid
- as part of other testing such as the biophysical profile
- to determine the position of a fetus
- to assess the placenta
How is an ultrasound scan performed?
Although the specific details of each procedure vary slightly, generally, ultrasounds follow this process. Two types of ultrasounds can be performed during pregnancy:
- abdominal ultrasound
- In an abdominal ultrasound, gel is applied to the abdomen and the ultrasound transducer glides over the gel on the abdomen to create the image.
- transvaginal ultrasound
- In a transvaginal ultrasound, a smaller ultrasound transducer is inserted into the vagina and rests against the back of the vagina to create an image. A transvaginal ultrasound produces a sharper image and is often used in early pregnancy.
Ultrasound images may be captured in still photographs or on video to document findings.
Ultrasound is a technique that is constantly being improved and refined. As with any test, results may not be completely accurate. However, ultrasound can provide valuable information for parents and medical providers to help manage and care for the pregnancy and fetus. In addition, ultrasound gives parents have a unique opportunity to see their baby before birth, helping them to bond and establish an early relationship.