A fetal ultrasound, or sonogram, is an imaging technique that uses high-frequency sound waves to produce images of a baby in the uterus.Fetal ultrasound images can help your health care provider evaluate your baby's growth and development and determine how your pregnancy is progressing. A fetal ultrasound might also give you the chance to study your baby's profile months before delivery. In some cases, fetal ultrasound is used to evaluate possible problems or confirm a diagnosis.Fetal ultrasound is often done during the first trimester to confirm and date the pregnancy and again during the second trimester - between 18 and 20 weeks - when anatomic details are visible. If your baby's health needs to be monitored more closely, ultrasounds might be repeated throughout the pregnancy.