A pregnancy ultrasound, or sonogram as it is sometimes called, is a test that uses sound waves that are bounced off solid objects to produce a picture. Ultrasounds are used in pregnancy to see how well the fetus is developing inside the uterus.
There are many different ways that ultrasound may be utilized in pregnancy. The first is the abdominal ultrasound where the ultrasound probe is placed directly on the abdomen by the sonographer. This approach is commonly used after the 12 week point when the woman’s uterus has enlarged outside the pelvis. The frequencies of ultrasound waves used at this point are in the 3.5 to 5.0 MHz range and are delivered by intermittent pulsation.
Vaginal ultrasounds are commonly used before the 12 week point to evaluate and confirm an early pregnancy. A sterile probe is placed in the vagina and sound waves are delivered by intermittent pulsation in the range of 5.0 to 7.5 MHz. The vaginal obstetric ultrasound procedure is not dangerous and will not cause miscarriage. The vaginal obstetric ultrasound has become more common in the last few years.
The Doppler ultrasound emits continuous sound waves that are used to detect blood flowing through the umbilical cord to the fetus. The Doppler is also capable of evaluating the blood flow between the uterus and the placenta. Both of these tests can tell much about the health of the developing infant and the uterus. Doppler ultrasound in early pregnancy can be used to predict congestive heart failure in the developing infant and predict possible miscarriage. Over 99 percent of pregnancies with an abnormal Doppler obstetric ultrasound will end in miscarriage.
A more recent development is Doppler angiography that allows for visualization of the smaller fetal blood vessels. However, this type of technology is not used unless the physician strongly suspects some type of fetal abnormality.
Another advance in obstetric ultrasound is the ability to use sound waves to detect the baby’s heartbeat. After the 12 week point, a portable, hand held Doppler can be used to direct sound waves of approximately 2MHz through the abdomen and pick up the sound of blood flowing through the baby’s heart.
One of the most exciting advances in ultrasound imaging has been the use of 3D and 4D obstetric ultrasound imaging. 3D ultrasound works by using thousands of sound waves in a series that produces a life-like image of the developing infant. With 4D sonogram, the movements of the infant can be studied, somewhat like watching a movie. For most patients, traditional ultrasound will be all that the doctor will need to evaluate the health and development of the infant.
Ultrasound scans can also be used to evaluate for the presence of ultrasonic soft markers. These signs picked up on obstetric ultrasounds can be indicators of fetal malformations such as Down’s syndrome or Spina Bifida. Follow up with 3D ultrasound can give the physician more information about the extent of the fetal problems.
Ultrasound technology is also used to assist the obstetric physician in performing other diagnostic procedures such as in utero blood transfusions, amniocentesis, cord blood sampling, and chorionic villus sampling.