Women's Health Specialists of St. Louis
Obstetrics and Gynecology

Articles - Ultrasound in Pregnancy

Thirty or so years ago, mothers did not have the option of ultrasound in pregnancy. Now with advances in technology, ultrasounds or sonograms have become the standard of care. Ultrasound is a useful tool for monitoring the health of the unborn baby and allows parents a peak at their unborn child. The terms ultrasound and sonogram are used interchangeably and both refer to the use of sound waves to create a picture. The term ultrasound means to use high frequency sound waves. The term sonogram means to create a picture using sound waves. Ultrasound can generate sonogram pictures by bouncing the sound waves off of tissues. The only danger in ultrasound is that energy from the sound waves also causes the tissue that is being looked at to vibrate. With vibration heat can be generated. This has been extensively studied to establish the safety of ultrasound in pregnancy. Ultrasounds used for pregnancy are designed to use the least amount of energy possible and to not raise the temperature of the baby or surrounding tissues. In fact, the standard ultrasound transducer used in pregnancy would have to be held in one place for over 2 hours before any dangerous rise in temperature would occur. Many of the new ultrasound machines now have measuring devices to calculate an estimate of heat generated to further reduce this risk.

Most women will receive two ultrasounds during their pregnancy. The first ultrasound is generally performed in the first trimester between 8-13 weeks. The first trimester ultrasound is an invaluable tool for predicting the due date and is considered to be more accurate than the estimate by last menstrual period. In fact, if the due date estimated by the last menstrual period is more than seven days different than that estimated by the first trimester ultrasound, then the due date is changed. Ultrasound performed later in pregnancy becomes less accurate for predicting the due date so once a due date is set by a first trimester ultrasound then it is not changed. First trimester ultrasound can now also be used as a screening tool for Downs syndrome and other chromosomal abnormalities. During a first trimester ultrasound performed between 10 weeks and 13 weeks 6days a nuchal translucency or measurement of an area on the neck of the baby can be used to help screen for genetic disorders.

The second trimester ultrasound is certainly the most anticipated and enjoyable ultrasound for parents to see. This ultrasound is generally performed in the fifth month or around 20 weeks of gestation. Waiting until this time allows the baby to grow and develop so that the heart, brain, and other vital structures can be evaluated. It is also a time when parents, if they chose, can find out the sex of their unborn child.

Though most women will have only two ultrasounds during their pregnancy, ultrasound may also be performed to monitor the growth and status of the baby if there is a specific concern. Many parents request ultrasounds when they have concerns about their unborn child and many parents are now inquiring about new 3D and 4D ultrasound. This newer technology does provide a slightly better picture of the outside of the baby but unfortunately does not usually provide medically useful information. The pictures are enjoyable for parents to see but do not provide any additional benefit over traditional ultrasound. For this reason, most obstetricians do not currently offer nor recommend 3D or 4D ultrasound because of the fear that parents will have false reassurance that their baby is well. There are locations where these ultrasounds may be performed for entertainment purposes only. They are considered safe to perform but should be considered as babys first photo rather than a medical ultrasound.