Prenatal Ultrasound

A prenatal ultrasound (also known as a sonogram) is a non-invasive imaging technique that gives doctors an accurate picture of a fetus. An ultrasound can be performed at different times during pregnancy to identify potential fetal conditions or congenital anomalies. It also provides information that helps patients and their providers manage care for the pregnancy and the fetus.

Ultrasonography uses high-frequency sound waves to make 2D, 3D, or real-time moving images. Ultrasound is painless, produces no radiation, and has no harmful effect on a fetus or pregnant person.

During a prenatal ultrasound, sound waves pass through the skin, uterus, and fetus. These waves bounce off bone and soft tissue, creating echoes detected by the ultrasound transducer. These echoes are analyzed by the ultrasound machine computer to form an image.

Your ultrasound exam may include fetal Doppler ultrasound, which visualizes and measures blood flow patterns in the fetus.

• Waveforms of the blood flow are shown on the ultrasound screen.
• A computer collects and processes the sounds and creates graphs or color pictures that represent the blood flow through the blood vessels.

At the Fetal Care and Surgery Center, we perform prenatal ultrasounds using state-of-the-art equipment. This advanced technology allows us to obtain incredibly detailed 2D and 3D images of the smallest structures, examine blood flow, and provide a comprehensive view for patients and their doctors.

Whether it’s routine care or uncovering rare conditions, the multidisciplinary teams at Boston Children’s are equipped to offer unparalleled expertise in diagnosing and treating diseases and conditions affecting fetuses, newborns, infants, and children, including:

• Complex multiple gestation
• Congenital diaphragmatic hernia (CDH)
• Cleft lip and palate
• Clubfoot
• Genetic conditions
• Kidney blockage and lower urinary tract obstruction
• Neural tube disorders such as spina bifida
• Abdominal wall defects, including gastroschisis and omphalocele

Times during pregnancy when a prenatal provider may recommend an ultrasound:

First trimester

• Establish the dates of a pregnancy
• Document the heartbeat
• Determine the number of fetuses
• Identify placental structures
• Detect fetal abnormalities
• Diagnose an ectopic pregnancy or miscarriage
• Examine the uterus and other pelvic anatomy

Mid-trimester (18-to-22-week scan)

• Confirm the dates of a pregnancy
• Determine the number of fetuses
• Monitor fetal growth
• Assess fetal well-being
• Detect fetal abnormalities
• Check the amount of amniotic fluid
• Examine blood flow patterns of both the pregnant person and the fetus
• Assess the placenta
• Measure the length of the cervix
• Assist in prenatal procedures

Third trimester

• Monitor fetal growth
• Determine fetal position
• Assess fetal well-being, which may include a biophysical profile
• Follow up on anomalies identified earlier
• Check the amount of amniotic fluid
• Assess the placenta
• Assess brain development

While details may vary procedure to procedure, prenatal ultrasounds generally follow these steps:

• Transabdominal ultrasound: Gel is applied to the abdomen, and the ultrasound transducer glides over the gel on the abdomen and pelvis to create the image.
• Transvaginal ultrasound: A sterile probe is inserted into the vagina and rests within the vagina against the cervix to create an image of the uterus and fetus.
  • A transvaginal ultrasound produces a higher-resolution image and is often used in early pregnancy.

A prenatal ultrasound uses an ultrasound machine, which is made up of the following parts:

• Transducer: A handheld device that emits and receives ultrasound waves. The transducer moves over the abdomen or, in some cases, inserted into the vagina (transvaginal ultrasound).
• Gel: A clear water-soluble gel is applied to the abdomen to help the transducer glide smoothly and improve the transmission of sound waves.
• Computer: The ultrasound machine is connected to a computer that processes the information received by the transducer and converts it into images that are displayed on a monitor.

The type of transducer and ultrasound machine can vary, and technological advances have led to high-frequency probes and advanced imaging capabilities for more detailed and accurate prenatal assessments. Additionally, the room used for scanning has dim lighting so that the pictures can be seen more clearly.

Prenatal ultrasound examinations are performed by a team of highly trained fetal sonographers supervised and interpreted in the Fetal Care and Surgery Center by pediatric radiologists, maternal fetal medicine specialists, and fetal surgeons. These professionals are experts in fetal imaging, and their diagnoses guide treatment before and after birth.

At the Fetal Care and Surgery Center, we also use prenatal ultrasound to help guide some procedures in the operating room, including fetal surgery and prenatal genetic testing such as amniocentesis and chorionic villus sampling (CVS).