Ultrasound is the most commonly used modality in pregnancy to image the unborn fetus and determine the health of the pregnancy. Across each trimester, ultrasound is used to enhance safety for the mother and provide reassurance regarding the fetal well-being. Current ultrasound technology allows for traditional two-dimensional (2D) imaging as well as the more recent 3D and 4D (or 3D in motion) evaluations. Ultrasound is generally considered safe in pregnancy for medical diagnostic purposes with focused evaluations. The safety of unnecessary prolonged ultrasound exposure for entertainment purposes has been poorly studied in in the medical literature and not currently advocated by national organizations (AIUM, ACOG, SMFM).
In the first trimester, ultrasound is used to identify the location, viability, and number of fetus(es) present. Most importantly, it confirms the gestational age of the pregnancy to allow for proper timing of care throughout the pregnancy. Finally, screening for chromosomal/genetic problems can be provided to patients if desired through various nuchal translucency screening programs. In the second trimester, ultrasound is used to evaluate the fetal anatomy and possibly to evaluate the cervical length as a marker of risk for preterm birth often based upon risk factors. In the third trimester, ultrasound is used to assess fetal growth and well being based upon various clinical indications to be reviewed with individual care providers. If fetal growth is determined to be poor, often physicians may evaluate the blood flow in the umbilical cord in order to determine the health of the placenta. Ultrasound is also used to guide the specialist performing invasive testing such as CVS (evaluation of placental tissue)/amniocentesis (evaluation of fluid taken from the sac surrounding the baby) in order to obtain a genetic sample of tissue.
We advise our patients to prepare for the testing by wearing loose fitting, generally two-piece outfits for the examinations. In general, only the abdominal area needs to be exposed during the procedure which is often painless. Often in the first trimester, transvaginal ultrasound may be required in order to evaluate the early pregnancy, or in the second and third trimesters to more accurately measure the cervical length in appropriately determined patients. Clear Ultrasound gel is used on the abdomen to allow the transducer to make secure contact with the skin, thereby providing a continuous path for the sound waves to enter the body. Images are captured on a screen and are interpreted by trained medical professionals. The pictures can be printed or electronically sent to various multimedia platforms for keepsakes. Transvaginal imaging inserts a narrow endocavitary probe specifically developed for this imaging modality. A protective disposable plastic cover is used over the transducer, lubricated with a small amount of gel, and then placed in the lower part of the vagina. This type of imaging is performed in the traditional gynecologic position, patients lying on their backs with both legs placed in foot rests (aka stirrups). Ultrasound images are generally completed within 30 minutes and patients can immediately resume normal activity. In some centers, the physicians interpreting the results will share their findings, while in other centers the physicians will simply send a report to your care provider and they will review the findings with you.
There are no known or proven harmful effects of medical diagnostic ultrasound to human fetuses when using standard clinical settings on the machines.
Additional resources on ultrasound imaging:
- FDA Consumer Update on Ultrasound (https://www.fda.gov/ForConsumers/ConsumerUpdates/ucm095508.htm)
- AIUM (http://www.aium.org/resources/statements.aspx)
Maternal Fetal Medicine blogs are intended for educational purposes only and do not replace certified professional care. Medical conditions vary and change frequently. Please ask your doctor any questions you may have regarding your condition to receive a proper diagnosis or risk analysis. Thank you!