Ultrasound is high frequency sound wave which is beyond human capacity for hearing. Current ultrasound technology works by transmitting this sound wave through the body and detecting echoes returning from different tissue densities. There is no ionizing radiation involved as in x-ray. Current understanding suggests that ultrasound poses no detectable risk to either fetus or mother. However, that is not to say that future studies will not discover new risks. Moreover, a developing fetus is inherently more fragile and more susceptible to external forces and should be treated with more care. Consequently, in ultrasound we follow the ALARA principle (As Low As Reasonably Achievable) - using the minimum power level and time needed to complete each ultrasound scan.
At the appropriate time of gestation and with baby’s cooperation, we should be able to identify most of the baby’s internal structures with 2D ultrasound. The 3D ultrasound complements this by giving us a better surface picture making it easier to visualize the baby’s face, extremities, and sex. The difference between the 2D and 3D ultrasound is similar to the difference between x-ray and photographs. One is designed to view the internal organs; the other is for looking at the surface. Please note that sometimes due to the baby's size, gestational age, position, and maternal body habitus we will not be able to perform an adequate exam. Sometimes when the legs are crossed for example, we will not be able to determine the baby's sex. In these situations, we will ask patients to return another day when hopefully fetal position will have changed and organ development will have further matured. We will not charge for the follow up visit.
Like all medical diagnostic tests, ultrasound is a tool used to detect a specific set of
abnormal conditions; it will not detect anything outside of that set of conditions.
Conditions currently detectable to a varying degree by 2D ultrasound includes neurotube
defect (e.g. spina bifida, anencephaly, hydrocephaly), cleft palate, cardiovascular
malformation (e.g. heart defect), diaphragmatic hernia, omphalocele, gastroschesis,
growth restriction, macrosomia, cervical incompetence, placenta previa,
oligohydramnios, Down syndrome, trisomy 13, trisomy 18, etc. This list is by no means
exhaustive, but it does demonstrate the extensive set of conditions that we must look for
specifically during each real-time 2D ultrasound. Unfortunately, the list of diseases not
detected (e.g. sickle cell disease, muscular dystrophy, mental retardation, cerebral palsy,
etc.) is exponentially longer. Color doppler contribute to the evaluation of in utero fetal
well being by determining blood flow through specific fetal blood vessels. And, the 3D
ultrasound is by design useful to detect only surface defects such as cleft lips,
omphalocele, gastroschesis, and neurotube defects.
On each pregnancy, we like to perform three ultrasounds. The first ultrasound is performed endovaginally at 6 - 12 weeks looking at fetal number and age. Between 11-13 weeks we perform a nuchal translucency ultrasound (a marker for Down syndrome). The second (abdominal real-time 2D) ultrasound is performed at 20-22 weeks looking for central nervous system, cardiac, abdominal wall, urinary system abnormalities as well as placental placement, umbilical vessels, and cord insertions. This is also a good time for measurements of fetal biparietal diameter, head circumference, abdominal circumference and femur length to ascertain appropriate fetal growth. If the baby is cooperating, we may be able to glimpse at the sex at this time. We like to perform the 3D ultrasound at 28-35 weeks as this is the best time to obtain images of the face looking for clefts, and of limbs looking at toes and fingers. We will also perform a 2D scan at this time to confirm appropriate growth, check placental placement and adequacy of amniotic fluid. Additional ultrasound scans are performed throughout pregnancy with appropriate medical indication.
Unlike CT scan or colonoscopy, there is relatively little preparation. You do not have to fast and you do not have to have a bowel prep. You may or may not have to come with a full bladder depending on the study scheduled. You will be instructed at the time you schedule your appointment. We do recommend that you wear loose comfortable clothing
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