An ultrasound exam is a type of advanced imaging technology. An ultrasound can produce a 2-D black, grey, and white image of your internal state using sound waves. Ultrasound exams are often used in obstetrics to see how a woman’s ovaries and uterus are responding to fertility and other treatment, and to view the development of a fetus.
How does an ultrasound work?
Your OB-GYN will direct soundwaves towards the area of your body to be viewed with a wand-like instrument called a transducer. The transducer emits very high-frequency soundwaves which can travel easily through your pelvis. The soundwaves bounce off the fluids, tissues, and bones, which allows the transducer to detect their size, shape and location. This is not unlike dolphins’ ability to sense their surroundings using echolocation.
During your exam, you’ll be able to view the images on a screen, aggregated to show motion. You can also take home still-frame “photos” of your growing baby if you wish.
What can an ultrasound show?
An ultrasound can tell your doctor a lot about the fetus and your pregnancy, including:
- Its size and approximate age
- Its position and orientation in your uterus
- Its heart rate and respiration
- The volume of amniotic fluid
- The location and size of the placenta
An ultrasound can also tell whether you are carrying a multiple pregnancy (twins, triplets, or more). It can also screen for certain birth defects or ectopic pregnancy.
Other non-obstetrical uses for an ultrasound exam include diagnosing tumors, cysts, and polyps, and rooting out causes of pain and menstrual problems.
Are there different types of ultrasounds?
Yes. Each type of ultrasound was developed to better provide your doctor with the type of image needed to evaluate your condition.
For this type of ultrasound, your OB-GYN will squirt an amount of clear jelly on your belly and glide the transducer across the abdomen. The jelly acts as a soundwave conduit between the transducer wand and your tissue. You should wear a loose-fitting shirt and drink plenty of water a few hours before your transabdominal ultrasound. Drinking fluids will fill your bladder, pushing the uterus up past the bowels and towards the abdominal wall, making the fetus easier to see.
In this procedure, the transducer wand is inserted into your vagina. This type of ultrasound can generally see more of your pelvic organs than a transabdominal ultrasound, and may be more useful in the first trimester when the fetus is still very small. You will be asked to undress from the waist-down, and to lie on your back and place your feet in the stirrups, much like during a normal pelvic exam. The transducer will be covered in a lubricated latex sleeve to make it easier to slide into your vagina.
3-D and 4-D ultrasound
These are transabdominal ultrasounds that take hundreds of images simultaneously, and aggregate them into a three-dimensional model, with or without showing movement.
A Doppler ultrasound can detect the circulation of blood in the placenta and umbilical cord. This is the type of ultrasound that can allow you to hear your baby’s heartbeat.
This is a type of transvaginal ultrasound that uses fluid to view the uterine cavity in greater detail. High-contrast saline solution will be injected into your uterus through a catheter placed in the cervix. You may experience some cramping during the procedure. Afterwards, you can expect some watery discharge as the fluid leaves your uterus through your vagina. You can wear a pad to soak up the fluid.