Ultrasound and pregnancy

Ultrasound is a test that uses high-frequency sound waves to create an image of internal body parts.


Purpose
When used during pregnancy, an ultrasound can provide important information about the baby and maternal pelvic structures, such as the uterus (the organ that houses the baby during pregnancy) and placenta (the structure in the womb that nourishes the baby and helps him or her discard waste). The sound waves can be directed through the abdominal wall or through the vagina.

Indications
Ultrasounds can help the doctor monitor your health and your baby's health from about the 5th week of pregnancy until delivery. There are many uses for the test, including:
verifying pregnancy
determining the number of fetuses
determining fetal age, growth, position and movement
monitoring the position and the condition of the placenta
assessing the amount of amniotic fluid
identifying certain birth defects, such as neural tube defects (affecting the spinal cord or brain), heart defects and abdominal defects
identifying an ectopic pregnancy (when the fertilized egg develops outside the uterus)
evaluating vaginal bleeding and abdominal pain
obtaining further information following an abnormal test, such as a maternal serum screening for certain birth defects
locating the best area for testing during chorionic villus sampling (taking a small sample of the chorionic villi -- small projections of placental tissue that attach the membrane of the embryo to the wall of the uterus -- for microscopic evaluation) and amniocentesis (withdrawing a sample of amniotic fluid -- the fluid that surrounds and protects the baby in the womb -- for examination)
Depending on the reason, ultrasounds may be done once or periodically throughout the pregnancy. Although the baby's sex can sometimes be determined through ultrasound, that wouldn't be sufficient reason to do an ultrasound. If you're having an ultrasound and don't want to know your baby's sex, tell your doctor and the ultrasound technician in advance.


Patient preparation
If you're having an abdominal ultrasound, you may be instructed to arrive for the test with a full bladder. Drink three to four glasses of water an hour before the test and don't urinate before the appointment. If you're having a transvaginal ultrasound (in which the sound waves are directed through the vagina), a full bladder isn't necessary.

Procedure
If you're having an abdominal ultrasound, you'll be asked to lie on your back. A gel that helps transmit sound waves will be applied to your abdomen. Then, an instrument called a transducer will be moved over your abdomen. The sound waves will be recorded, and the picture of your uterus and baby will appear on a monitor. The procedure usually takes about 20 minutes, but in some cases it may last up to an hour.
A transvaginal ultrasound is similar to an abdominal ultrasound. Rather than running the transducer over the abdomen, however, a probe that serves as the transducer is gently inserted into the vagina. This type of ultrasound is usually done only during the first trimester.


Postprocedure care
Discuss the test results with your doctor and ask if you'll need any additional tests.

Benefits
Ultrasound doesn't use X-rays to produce an image, and the test is painless for you and the baby. An ultrasound can provide you with reassurance that your pregnancy is progressing normally or offer information that's helpful in making important treatment decisions.

Risks
Ultrasound has been used in obstetric care for more than 30 years. There have been no cases of documented harm to mother or baby. To avoid any possible risk, however, it's recommended that ultrasounds during the first trimester be done only when necessary. Also, ultrasound isn't 100 percent accurate. Ultrasounds can be used to rule out many abnormalities, but some abnormalities can't be detected and others may not develop until later in the pregnancy.