Relax -- You don't have to brace for needles when you get this painless test. During an ultrasound your doctor or a skilled technician uses a plastic transducer to transmit high-frequency sound waves through your uterus. These sound waves send signals back to a machine that converts them into images of your baby.
The standard ultrasound arms your doctor with valuable information. It allows him to monitor your baby's growth and track milestones, detect abnormalities, home in on your due date, determine whether you're carrying multiples, see the position of your placenta (important for delivery), and (a big one for parents-to-be!) make out the sex of your baby.
Another exam that utilizes ultrasound is Doppler fetal monitoring. This test is typically performed during the last trimester on women who suffer from gestational diabetes. A regular ultrasound uses sound waves to produce images; this one bounces high-frequency sound waves off circulating red blood cells to measure blood flow and blood pressure. The test will determine if Baby is getting enough blood.
An ultrasound is considered safe for both you and your baby when it's used for medical purposes. A trained professional who can interpret the results with accuracy and who is a pro at detecting abnormalities should perform it. Your technician should be schooled in obstetrical ultrasound, preferably at a center accredited by the American Institute of Ultrasound in Medicine. Unlike X-rays, an ultrasound involves no radiation.