Ultrasound in Pregnancy

What is ultrasound scanning?

Ultrasound scanning is a procedure that uses sound waves to create a picture of organs in the body.

When is it used in pregnancy?

Ultrasound scanning examines your unborn baby, your uterus, amniotic sac, placenta, and ovaries.

A routine scan is usually done early in the pregnancy to confirm your due date. Between 11 and 13 weeks a scan may be done as part of genetic testing for Down Syndrome. Around 20 weeks a scan is done for a general overview of the baby’s anatomy. We also may use it if we suspect a problem with the pregnancy or if you have risk factors that could lead to problems for the baby.

Ultrasound scanning is used in pregnancy to:

  • Make sure the baby is developing in the uterus and not inside a fallopian tube (ectopic pregnancy).
  • Determine how far along you are in your pregnancy.
  • Check that the baby is growing normally.
  • Estimate the weight of the baby.
  • See if the placenta is normal and attached properly.
  • Check the position of the baby in the uterus.
  • See if the baby's body has any major problems.
  • Check the amount of fluid around the baby inside the uterus.
  • Check the baby for signs of stress as part of a biophysical profile.

An ultrasound scan may be done for different reasons at different stages in the pregnancy. For example, tests to see if the baby is growing at a normal rate are most accurate during the second trimester of pregnancy. To check the age of the baby or check for more than one baby, an ultrasound is often done before the 12th week.

How do I prepare for ultrasound scanning?

Early in pregnancy, a full bladder may be helpful to see the baby. Drink 4 glasses of non-carbonated fluids about an hour before the exam, and do not empty your bladder until told to do so. Usually, no special preparation is necessary for a routine ultrasound after 16 weeks gestation.

What happens during the procedure?

A device called an ultrasound transducer is used to do the scan. The transducer acts like a microphone. During the scan, sound waves enter your body and are reflected by the organs and create echoes. The transducer is connected to a computer. The computer analyzes these echoes and produces images of the organs on a screen.

The abdominal ultrasound exam will be done by first putting an ultrasound gel on your abdomen and then moving the transducer over your belly. Some ultrasound exams, especially early in pregnancy, are done through the vagina. For these scans the transducer is shaped like a narrow tube and covered with a condom-like sheath. It is inserted gently into the vagina.

An ultrasound scan does not hurt you or your baby. It takes about 30 to 45 minutes. You can watch the images of your baby on the screen, and will be given copies of printed pictures as keepsakes. These pictures are subject to fading, so keep them away from direct sunlight and consider scanning them onto a digital media.