Fetal Ultrasound

What is an ultrasound?

An ultrasound examination (or sonogram) consists of an imaging technique that generates a high-quality image of the developing fetus within the uterus


Why is an ultrasound performed?

Many birth defects, such as spina bifida, heart defects, brain abnormalities, cleft lip, club foot, chest, abdominal and genitourinary abnormalities can be diagnosed by a fetal ultrasound. If the abnormality exists, pediatric subspecialists including heart surgeons, orthopedic surgeons, craniofacial surgeons, neurosurgeons or intensive care specialists can meet with the expecting parents to help them understand the course of medical care once the baby is born. In certain cases, the specific abnormality may require pediatric subspecialty care to be present at the time of delivery.


Why can’t I have my ultrasound performed in my obstetrician’s office?

While simple ultrasounds can be performed by an obstetrician/gynecologist, first trimester nuchal translucency screening, detailed anatomic surveys, diagnostic procedures, and comprehensive evaluation/monitoring of fetal health require specialized ultrasound equipment and subspecialty training in the field of Maternal-Fetal medicine.


When is a fetal ultrasound performed?

First Trimester
The two most common indications for a fetal ultrasound in the first trimester are to confirm a viable pregnancy and to undergo a nuchal translucency measurement. While the confirmation of a viable pregnancy is usually performed in the primary obstetrician’s office, the nuchal translucency measurement that requires specialized training and high-resolution ultrasound performed by a maternal-fetal medicine specialist.

Second Trimester
The most common ultrasound performed in the second trimester is a detailed anatomic survey. This study, usually performed between 18-20 weeks, evaluates the fetal anatomy in detail, looking for abnormalities in genitourinary, gastrointestinal, cardiovascular, skeletal and central nervous system.

Third Trimester
Ultrasounds performed in the third trimester are usually performed to monitor fetal growth and health. This is typically accomplished by carefully measuring the fetal biometry amniotic fluid, and biophysical profile of the developing fetus. In the event additional information in needed for reassurance, sophisticated ultrasound techniques to interrogate fetal blood waveforms and flow velocity in various blood vessels can be employed.


Why do I need an ultrasound if my serum screening, non-invasive prenatal test (NIPT), CVS or amniocentesis was normal?

Screening tests such as the California Prenatal Screening Program, non-invasive prenatal tests (NIPT) qualify risk for a few chromosome abnormalities. Even in the setting of normal screening results or diagnostic testing – anatomic abnormalities can still occur.


If I have a non-invasive prenatal test should I still have a nuchal translucency (NT)?

Absolutely. It is unfortunately a common occurrence that abnormalities are found in the setting of normal test results. We would much rather identify and discuss those abnormalities at 11-14 weeks rather than 20-22 weeks.


If I am not interested in pursuing any prenatal screening – why should I undergo a nuchal translucency exam?

The NT exam is done between 11-14 weeks gestation. Even if a woman is not interested in undergoing any screening or diagnostic testing – the NT exam gives us valuable information about correctly dating a pregnancy and identifying potential interventions that may benefit your developing baby.


Does ultrasound pose any risks to my developing baby?

No. Ultrasound technology is amazing. The probe that is used to generate the ultrasound image emits an ultrasound wave that reflects off of the developing fetus to help generate a high-resolution image. The amount of time the probe emits sound waves is approximately 1/1000 of the time it spends listening. That means that if the ultrasound exam were to last 24 hours, the fetus would be exposed to roughly 1 minute of ultrasound energy.


Why should I have my ultrasound performed by Diablo Valley Perinatal Associates?

We are a specialized referral center that performs more than 18,000 fetal ultrasounds each year. Our sonographers and physicians are specifically trained to obtain and interpret fetal images. We perform more fetal ultrasounds than most university based Maternal-Fetal medicine divisions in the United States.

Why is an ultrasound exam so important in pregnancy?

During the first trimester, a fetal ultrasound accurately assigns the gestational age of a pregnancy.  It is also the time when the health of an early pregnancy can be evaluated with the measurement of the nuchal translucency – a precise measurement of a “translucent” area on the back of the developing fetal neck (performed between 11-14 weeks).  This measurement, when performed in combination with a first trimester and second trimester blood test, provide a risk assessment for the most common chromosome abnormalities

During the second trimester, a detailed anatomic survey rules out most birth defects when done by a specialized perinatal center.  During that exam, stringent parameters are followed, established by the American Institute in Ultrasound Medicine (AIUM) regarding anatomic structures that must be evaluated – assuring to the limitation of ultrasound itself, you baby is thoroughly examined.

During the third trimester, a fetal ultrasound evaluates the size of the developing baby and identifies pregnancies with abnormal growth.  In the event of a growth abnormality, advanced imaging techniques including evaluation of blood flow velocities and wave forms through specific blood vessels in the brain,  heart, liver and umbilical cord can be undertaken.  In addition, biophysical parameters such as fetal breathing, tone and movement can also be used to determine the health of the developing baby in combination with a fetal non stress test.



A Perinatologist's Perspective:

Antenatal testing is without a doubt - inconvenient.  Twice weekly visits to undergo antenatal testing between 32 weeks and the delivery of your baby is a real time committment and disruptive to work, family and social calendars.  As care providers, we empathize.  But the benefits of antenatal testing far outweigh the horror of a stillbirth that may have been preventable.