Three-dimensional and four-dimensional ultrasounds Three-dimensional (3D) and four-dimensional (4D) ultrasounds are both sophisticated technologies that produce a more life-like image of the infant. The difference between the two is that 3D images are still photographs, while 4D images show the baby moving.

For example, 3D/4D ultrasounds give a better image of the baby’s features when a perinatologist is concerned about abnormalities of the lip, hands or feet. These more detailed images may also help you understand what the physician is seeing.

How Is an Ultrasound Performed?
During this painless procedure, a transducer, something like a computer mouse in size, is lightly passed over your abdomen, putting out very high frequency sound waves. The waves are reflected back to the transducer and are turned into a picture on a monitor.

What Information Can an Ultrasound Provide?
An ultrasound can provide early confirmation of pregnancy. It can diagnose ectopic or tubal pregnancy (where the pregnancy is implanted within the fallopian tube rather than the uterus) or determine if a miscarriage is occurring. As your baby grows, ultrasound can be used to measure the size of his or her head, femur (long leg bone), and abdominal circumference. An ultrasound can provide clues about the health of the baby by looking closely at the developing organs. It can also diagnose multiple pregnancies, and it can often show whether your baby is a boy or a girl, if you wish to know in advance.

Ultrasounds may be performed at about:

• 6-7 weeks or later to confirm pregnancy and estimate birth date
• 18-20 weeks to scan for birth defects and measure the baby for growth and development
• 34 weeks to evaluate the baby's size and growth again.
• Other scans may be done as needed if further assessment or diagnosis is required.

Safety
In the five decades since the first ultrasounds were performed on pregnant women, there have been no confirmed reports of harm to either the mother or the baby from ultrasound waves.