What happens when I get my first ultrasound?
Ultrasound uses sound wave to create pictures of the fetus as it grows and develops in the uterus. The ultrasound transducer (also called a probe) sends out sound waves (like sonar, pitched too high for our ears to hear) and then listens for the echoes as the waves reverberate off the tissues underneath. The ultrasound computer then uses the echoes to generate a black and white moving picture on a TV screen.
Getting an ultrasound is usually a very exciting moment for a pregnant woman and her partner or family. Some people think of it as their baby's first photo and even frame a printout from the television monitor or hang it on the refrigerator. When ultrasounds are obtained because of a problem, howeverâ€”for example when bleeding early in pregnancy raises concern for a miscarriageâ€”ultrasounds can be filled with anxiety.
Fetal ultrasound is useful for:
Â· determining your pregnancy due date (if you are not sure when your last period started)
Â· evaluating the health and appropriate development of the baby
Â· estimating fetal weight
Â· determining fetal position (e.g. head down , head down, head sideways).
It can show some but not all birth defects. For example, most cases of spina bifidaâ€”failed closure of the spinal column with the spinal cord left open and exposedâ€”can be detected by ultrasound. More subtle abnormalities of the face and heart may be missed, however. Ultrasound also cannot detect problems that are not mirrored by differences in gross anatomyâ€”something has to "look" different to be seen. So ultrasound couldn't detect diseases like diabetes or sickle cell anemia.
For many genetic conditions, such as Down Syndrome, ultrasound cannot tell for certain if a condition is or is not present, but in some cases can detect subtle clues that will lead patients and providers to consider amniocentesis or other tests to determine for certain if the condition is present. Ultrasound is also useful for determining if you are carrying twins (assuming those doing it can count to two) and can sometimes give you information about the sex of your baby (unless you have a bashful child, sitting with legs crossed or closed).
Many women will have their first ultrasound between 18 and 20 weeks to evaluate fetal health and anatomy. Women with problems such as bleeding or pain will have an earlier scan. If your doctor suspects you are having an ectopic pregnancyâ€”meaning the fetus is developing in your fallopian tube instead of the uterusâ€”you may get an ultrasound around the time you first discover you are pregnant.
Some patients will choose to have an ultrasound in the first trimester as part of screening to evaluate their individual risk of carrying a pregnancy with conditions like Down syndrome. In the last part of pregnancy, if you have problems such as bleeding, high blood pressure, diabetes, too much or too little change in the size of your uterus, or concern about too little fetal movement, your provider might recommend and order further ultrasounds.
What happens during the ultrasound?
You will lie on your back on a table for the test. In the past, having a full bladder was needed but with changes in machines and technologies, this is generally not the case. A technician or doctor will squirt some clear jelly onto your lower abdomen to help the ultrasound sensor slide around easily and conduct the ultrasound waves to the underlying tissues, and then will place the sensor against your skin in this jelly. The examination should not be painful. When the sensor is in place, a picture will appear on a TV screen, and the technician or doctor will move the sensor back and forth on your abdomen to see the fetus from many different views. Depending on the age of the fetus, the heartbeat, movement of arms and legs, and many of the internal organs may be visible. Sometimes, in order to better visualize an early pregnancy or look specifically at the lower part of the uterus and cervix, a transvaginal ultrasound may be recommended. For transvaginal scans a probe with a sterile cover is placed inside the vagina.
A doctor (sonologist) interprets your ultrasound images, but the images themselves may be obtained by a technician (sonographer). Depending on whether the person in the room performing the ultrasound is a doctor or a technician, you might be able to get a few results of your test immediately. The images will be recorded electronically and reviewed by the sonologist (who may be an obstetrician or radiologist) and then reported to your doctor, a process that might take a day or two.
Have you had an ultrasound already? What was your experience like? If you haven't, do you have any questions about what the test will be like?
Jeffrey Ecker, M.D., is an attending perinatologist (high-risk obstetrician) at Massachusetts General Hospital. He is also an Associate Professor at Harvard Medical School.
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