Fetal ultrasound uses reflected sound waves to provide an image of the fetus and placenta. Fetal ultrasound is the safest way to obtain information about the fetus, such as its size, position, age, and condition.

During a fetal ultrasound, a small hand-held instrument called a transducer is used to direct sound waves through the pregnant woman's abdomen. A computer analyzes the sound waves that are reflected back from the fetus and other structures in the uterus and converts them into an image. Fetal ultrasound can be done by moving the transducer across the woman's abdomen (transabdominal) or by inserting the transducer in her vagina (transvaginal). After about the 11th week of pregnancy, almost all fetal ultrasounds are done using the transabdominal method.