Renaissance Women's Group – Austin OBGYN

Obstetrical Diagnostic Ultrasound

Obstetrical Diagnostic Ultrasound Is a Valuable Tool for Moms-to-Be

Obstetrical diagnostic ultrasound is an important medical diagnostic test used by our Austin obgyns during a patient’s pregnancy. Diagnostic ultrasound is used for many different reasons at different times during pregnancy, based on the individual’s needs.

There are no risks that we know of to mother or baby from diagnostic ultrasound, but it is a medical test which is not ordered without indications.

First Trimester Diagnostic Obstetrical Ultrasound

Ultrasound in the first trimester can be done for many reasons. We frequently perform an ultrasound at your first or second visit early in pregnancy to confirm that the due date is correct, that the embryo or fetus is viable, and that it is a single or twin pregnancy. Other common reasons for early pregnancy ultrasound are bleeding or pain early in pregnancy, which might indicate a possible miscarriage or ectopic (tubal) pregnancy.

Screening for Fetal Chromosome Abnormalities

Ultrasound can also be used to help assess risk for chromosomal abnormalities such as Down Syndrome (Trisomy 21) or Trisomy 18. For patients at low risk for chromosome problems (no family history, maternal age less than 35), we offer a test called “First Screen” at 11-14 weeks. This test utilizes an ultrasound exam which specifically measures a thin area of fluid behind the fetal head and neck, the “nuchal translucency” or “NT”. This NT measurement is combined with maternal age and the measurement of several maternal hormone levels to produce a statistical assessment of the risk of Down Syndrome and Trisomy 18. This test cannot determine if these conditions are actually present, but will allow us to identify pregnancies at high risk for these conditions, and then discuss tests which will give us a definite answer about whether a chromosome abnormality is present. The First Screen will detect approximately 85 to 90 percent of Trisomy 21 and 18. However the test also has a significant false positive rate, and fortunately most patients with a high-risk result do not actually have a fetus with a chromosome abnormality.

For patients who are high risk for chromosome problems, for example due to maternal age 35 or more, family history of chromosome problems, or a high risk on First Screen, we offer a new test based on fetal DNA contained in maternal serum. This Fetal DNA test, also called “Non-Invasive Prenatal Testing” or “NIPT” is an outgrowth of gene sequencing technology developed for the Human Genome Project. With this test, a fetal NT is performed with ultrasound, and a maternal blood sample is drawn. DNA sequencing technology is then utilized to test for Trisomy 21, 13 and 18 and X and Y chromosome abnormalities on fetal DNA that is present in maternal blood. The test is excellent at detection of these selected problems, with a very low false positive rate. At this time recommendations are that we reserve this test for high-risk situations, as the false positive rate increases in the low-risk population, and the test is significantly more expensive than First Screen.

The 20-Week-Anatomy Diagnostic Ultrasound Helps Us Evaluate Fetal Health

Although many people think of ultrasounds, or sonograms, during pregnancy as a way to see and share their baby’s image, it is something much more important than that for our obgyn team. We usually order a diagnostic ultrasound at 20 weeks gestation in order to evaluate the fetus and the mother, including:

  • Fetal anatomy—heart, lungs, other internal organs, spine, brain and limbs
  • Location of the placenta
  • Cervical length
  • Amount of amniotic fluid
  • Fetal activity

This ultrasound is known as a complete scan. If anything concerns our physicians, they may order a detailed scan to focus on a specific area.

Diagnostic ultrasound is a medical test that requires the sonographer’s full attention, so we do ask that no more than two people accompany the mother-to-be. We also do not allow children under six in the room during the test. We will give you a DVD with a few minutes of “baby pictures” that you can share with family and others if you wish.

Additional ultrasound exams

Ultrasound in the late second and third trimester is frequently used to monitor the pregnancy and fetus when there is a high-risk problem, or where there is a suspicion of a problem. Your physician will order these ultrasound exams should they be needed.

We Offer a Non-Medical, Family Bonding Ultrasound

When we perform a diagnostic ultrasound during your pregnancy, it is a medical test ordered for medical reasons; however, we understand that families may want to see their baby in a different way. We offer a Family Bonding Ultrasound, which is an optional, cash only, ultrasound that allows family members to enjoy the experience in a relaxed, non-medical context.

For more information about obstetrical diagnostic ultrasound, contact us. At RWG, we will help give you a clearer picture of your risks for fetal abnormalities during pregnancy.