The Importance of Ultrasound in Pregnancy

– by Sheryl Bashaw, RT, RDMS

   Ultrasound has been a phenomenal diagnostic tool since its discovery in 1951 by an English  physician named Ian Donald.  One year after its discovery, it was used on a pregnant woman.

   Ultrasound creates sound waves that enter the human body and bounce back, creating an image from the returning waves.  The low energy sound waves are not capable of changing cell structure and are safer than other forms of imaging.  In contrast, x-ray radiation, which is also called ionizing radiation, is capable of changing and damaging cell structure.  Therefore, ultrasound is the preferred method of visualizing many parts of the body. The FDA regards ultrasound as safe, but it must be ordered by a medical practitioner so that it is used appropriately. 

   At Pullman Family Medicine, we use ultrasound for many different reasons.  For the nonpregnant person it can be used to assess diseases of the abdomen, pelvis, breast, thyroid, testicle and soft tissue.

   The most popular use for ultrasound is in the evaluation of pregnancy.  Not only can ultrasound help us visualize a baby in utero but we can also look at the environment that helps sustain the baby (the cervix, placenta and amniotic fluid).

   First trimester ultrasounds are usually done to confirm viability and to check dates for gestational age.  We can see a gestational sac as early as 4-5 weeks after the last normal menstrual period.  At six weeks we can usually see a small fetal pole and heart beat.

   Between 11 weeks 0 days and 13 weeks 6 days, we can do an ultrasound called the Nuchal Translucency (NT) exam or Ultrascreen. In this optional ultrasound, we measure the Nuchal Translucency, which is a fluid filled sac that runs parallel to the spine. Statistics show that babies with Downs Syndrome (Trisomy 21) and Trisomy 18 have an unusually thick Nuchal Translucency. This measurement is used along with an analyzed blood sample to give us a more reliable test than the Quad Screen (which is traditionally done at 16 weeks) to determine these two abnormalities. The NT measurement should only be done by an ultrasound technologist who has been trained and certified in this measurement.  Our ultrasound technologist, Sheryl Bashaw, received her NT certification in February 2007, from the Fetal Medicine Foundation.

   In the second Trimester of pregnancy, at about 20 weeks, we can do a complete ultrasound evaluation of the baby. During this Fetal Survey we can evaluate the skeleton, heart, brain, organs and spine.  We can also evaluate amniotic fluid, placenta, umbilical cord and cervix. Other measurements are also done at this time to make sure that the baby is growing well.  At 20 weeks the baby’s body parts are large enough to see and the sound waves easily penetrate the bones.  As the baby matures, the bones become more calcified and the baby becomes more difficult to evaluate and measure.  We can often determine the sex of the baby during the Fetal Survey.  This is best accomplished on an active baby.  For best results, Moms are encouraged to not miss meals and to have a snack about half an hour before the ultrasound.

Moms are also often instructed to have a full bladder for their ultrasound. Although this can become uncomfortable, it is very important.  In the first trimester the full bladder helps push the uterus into a better position to view the baby and surrounding structures. Later, the full bladder helps us to measure the cervix. Once the cervix is measured, Mom should be free to empty her bladder.