What You Need to Know About the Safety of Prenatal Ultrasounds

It can be a joy to see your little gummy bear-sized baby bouncing on the ultrasound screen or figuring out whose nose baby has on a 3D scan. Most pregnancies require "routine" ultrasounds. Some pregnancies require extensive ultrasonography to ensure the health of your baby. Are prenatal ultrasounds safe? Should you consider reducing ultrasound exposure? What about "keepsake" scans?

Key takeaways:

What is an ultrasound?

Ultrasound is sound wave energy. The transducer of an ultrasound machine sends sound waves into the body. The sound waves bounce back, like an echo, when they encounter tissue, bones, and body fluids. The sound wave "echoes" transform into an image of your baby.

A Doppler ultrasound provides images of blood flow. During pregnancy, a Doppler ultrasound is used to evaluate the blood flow through the umbilical cord and other major blood vessels. The colors red and blue will appear on the screen to distinguish blood that is full of oxygen versus blood whose oxygen has been used by the body.

During pregnancy, three different types of ultrasound are performed:

  • Standard ultrasound. Evaluate your baby's physical development, including size and presence of congenital anomalies.
  • Limited ultrasound. Performed to answer questions such as the cause of vaginal bleeding, baby's position, or placenta location.
  • Specialized ultrasound. Used to assess a suspected problem or the potential for a complication, such as infant growth restrictions.

Why are ultrasounds performed during pregnancy?

Prenatal ultrasound imaging is used to see your baby while inside your uterus. Your provider can assess the health and development of your baby. Often, ultrasonography can detect congenital anomalies or other pregnancy complications such as placenta previa or twin-to-twin transfusion syndrome.

Obstetric providers perform ultrasounds with varying frequencies depending on the pregnancy. Low-risk pregnancies receive minimal ultrasounds. Higher-risk pregnancies may require more ultrasounds.

Routine prenatal ultrasounds

According to the American College of Obstetricians and Gynecologists (ACOG), every pregnant parent should have at least one prenatal ultrasound between 18 and 22 weeks pregnant to assess the developing baby's organs and limbs to identify any abnormalities. This standard ultrasound, commonly called the "anatomy scan," will also evaluate your baby's heart rate, movement, position, breathing, weight, amount of amniotic fluid, location of the placenta, and gestational age.

A first-trimester limited ultrasound may be performed around eight to 12 weeks to:

  • Confirm the number of weeks pregnant.
  • Evaluate for genetic disorders.
  • Assess the number of babies.
  • Confirm fetal heart rate.
  • Check for ectopic pregnancy.

As delivery approaches, your obstetric provider may also use ultrasound to confirm your baby's position, whether head down or breech position.

The results of a routine limited or standard ultrasound may indicate a need for more specialized and frequent ultrasounds. You may need more ultrasounds to:

  • Monitor multiple gestation pregnancy such as twins or triplets.
  • Evaluate vaginal bleeding.
  • Determine placental location, especially in the case of placenta previa.
  • Investigate fetal anomalies.
  • Determine cervical insufficiency.

Risks of prenatal ultrasound

ACOG has noted that no evidence suggests that ultrasound harms a developing baby. However, ultrasound is a form of energy with potential adverse health risks. The long-term effects of ultrasound exposure in humans have not been fully investigated. Therefore, ACOG recommended that only qualified individuals perform ultrasound when medically necessary.

What do the studies say about ultrasound safety?

The heat generated by ultrasound machines is the primary cause of concern. Boney areas of the baby, such as the skull and spine, are the most vulnerable to temperature increase. The detrimental effects of ultrasound's thermal or heat effects on animals have been studied.

Small studies have shown a correlation between increased body temperature in the pregnant person, such as fever, and congenital disorders. Specific human studies have not been done regarding the heat generated by ultrasound and negative birth outcomes or long-term conditions.

Human studies have shown no association between frequent prenatal ultrasounds and preterm delivery, induction of labor, APGAR scores, and vaginal or cesarean deliveries. Two 30-year-old studies did show an increase in perinatal deaths associated with increased prenatal ultrasounds, but the exact cause of death is unknown.

A retrospective study, or looking back at previous data, evaluated the severity of autism spectrum disorder (ASD) symptoms and the use of first-trimester ultrasound. This recent study did find that male children with ASD AND a genetic predisposition to ASD showed greater severity in ASD symptoms when they had first-trimester prenatal ultrasounds.

Studies have shown that routine prenatal ultrasounds in low-risk pregnancies do not improve infant outcomes.

Safety of "keepsake" ultrasounds

Improvements in ultrasound technology have led parents to seek out "keepsake" and 3D or 4D images of their growing little one. These images have been shown to help with parent bonding and provide reassurance of fetal well-being.

The American Institute of Ultrasound in Medicine (AIUM) and the Food and Drug Administration (FDA) recommend using ultrasound by credentialed sonographers for medical purposes only and under the guidance of a provider. This includes a recommendation against the use of at-home fetal Dopplers by parents.

Unfortunately, many keepsake ultrasounds are performed by uncredentialed technicians in freestanding imaging sites. These individuals may be unaware of the procedures regarding safe ultrasonography and could expose your baby to inappropriate amounts of sound waves. In addition to a lack of training, most of these facilities are not overseen by a specialized physician.

Freestanding fetal imaging sites or added-cost sonograms at credentialed facilities may violate medical ethics set forth by the American Medical Association (AMA) and ACOG.

How to get keepsake images of your baby

According to the AIUM, parents can request and receive images of their baby taken during medically-indicated ultrasounds throughout pregnancy. Ultrasound technicians are generally happy and ethically cleared to give parents a "keepsake" image of their growing baby in utero.

Tips to reduce ultrasound exposure

Properly trained sonographers should be aware of these principles:

  • Ensuring that the ultrasound machine is set to the lowest settings to get quality images.
  • Monitoring that the mechanical index (MI) and thermal index (TI) are the lowest necessary for the procedure.
  • Lifting transducer when still imaging is not necessary to reduce dwell time.
  • Keeping scanning time to a minimum to obtain necessary images.

As a parent, you can further reduce ultrasound exposure by:

  • Waiting. After an initial Doppler ultrasound to confirm a heartbeat, consider waiting until the second trimester for additional heartbeat checks with a fetoscope, a specially designed stethoscope.
  • Only have one. If your pregnancy is low risk, consider only having one ultrasound around 18 to 22 weeks.
  • Do not perform at home. Avoid at-home Doppler devices that allow you to check your baby's heartbeat on your own.

Ultrasound allows a "peek" inside your body to see your baby in real-time. However, such technology should be limited to necessity and respected for its potential risks. Resist the urge for those keepsake ultrasound pictures. Do not hesitate to speak with your obstetric provider about any concerns you have about prenatal ultrasounds.

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