Pregnancy: Prenatal Ultrasound
A prenatal ultrasound test uses high-frequency sound waves, inaudible to the human ear, that are transmitted through the abdomen via a device called a transducer to look at the inside of the stomach. With prenatal ultrasound, the echoes are recorded and transformed into video or photographic images of your baby.
The ultrasound can be used during pregnancy to show images of the baby, amniotic sac, placenta and ovaries. Major anatomical abnormalities or birth defects can show up on an ultrasound.
Most prenatal ultrasound procedures are performed topically, or on the surface of the skin, using a gel as a conductive medium to aid the quality of the image. However, a transvaginal ultrasound is an alternative procedure performed using a tubular probe that is inserted into the vaginal canal. This method of ultrasound produces an image quality that is greatly enhanced, but it is not a common prenatal procedure. However, it may be used early in pregnancy to get a clearer view of the uterus or ovaries if a problem is suspected. It may also be used early in pregnancy to determine how far along you are in your pregnancy (gestational age).
Is Prenatal Ultrasound Safe?
Studies have shown ultrasound is not hazardous. There are no harmful side effects to you or your baby. In addition, ultrasound does not use radiation, as X-ray tests do.
When Is an Ultrasound Performed During Pregnancy?
An ultrasound is generally performed for all pregnant women at 20 weeks gestation. During this ultrasound, the doctor will confirm that the placenta is healthy and attached normally and that your baby is growing properly in the uterus. The baby's heartbeat and movement of its body, arms and legs can also be seen on the ultrasound.
If you wish to know the gender of your baby, it can usually be determined at 20 weeks. Be sure to tell the health care provider performing the ultrasound whether or not you want to know the gender of your baby. Please note that ultrasound is not a foolproof method to determine your baby's gender; there is a chance that the ultrasound images can be misinterpreted.
An ultrasound may be performed earlier in your pregnancy to determine:
- Presence of more than one fetus
- Your due date or gestational age (the age of the fetus)
Later in pregnancy, ultrasound may be used to determine:
- Health of the baby
- Placenta location
- Amount of amniotic fluid around the baby
- Position of the baby
- Baby's expected weight
How Should I Prepare for the Test?
There is no special preparation for the ultrasound test. Some doctors require you to drink 4 to 6 glasses of water before the test, so your bladder is full. This will help the doctor view the baby better on the ultrasound. You will be asked to refrain from urinating until after the test.
Some doctors allow you to videotape the ultrasound so that you can take it home. Ask your doctor if this is an option. If it is, you will need to bring a blank videotape to your appointment.
Next: What happens during the test? »
- Pregnancy (Stages - Trimesters of Pregnancy) - Learn what to expect during the three phases of pregnancy (1st, 2nd, 3rd trimester). Find out what changes in your body to expect, and how your baby will develop week by week.
- Pregnancy Planning - The goals of pregnancy planning are to create a healthy environment for the fetus and to prevent birth defects and other pregnancy related problems.
- Birth Defects - Read about birth defects, the leading cause of infant mortality during the first year. Causes of birth defects include ingestion of drugs or alcohol during pregnancy, genetic, hereditary, or environmental factors.
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