During the course of your pregnancy, you will be required to go through numerous tests and examinations. While you may greet many of these with a degree of anxiety, the one that you will most likely look forward to is the ultrasound. This is the one you will eagerly anticipate because it will give you the first glimpse of your baby. MH finds out all about the ultrasound, how it is done, what it reveals and how mothers-to-be can prepare for them.
WORDS CONSTANCE NONIS
A woman usually undergoes a minimum of two ultrasounds during the course of her pregnancy although sometimes, she might undergo more. For instance, if she is experiencing spotting or bleeding, her doctor will usually perform an ultrasound to confirm the baby’s heartbeat is present and to check if the placenta is lying close to the cervix. If she is carrying multiples, serial ultrasound scans will be required to monitor the babies’ growth.
For most women, the first ultrasound scan will be in the first trimester. This will confirm viability of pregnancy and determine how many weeks the pregnancy is. From the latter, an expected due date for the pregnancy will be established.
A transvaginal scan is usually required if the pregnancy is less than 8 weeks. Beyond this gestation, a transabdominal scan will usually allow visualisation of baby, although ease of visualisation may be influenced by factors such as maternal habitus and whether the bladder is full or not (urine in bladder acts as “window” to visualise inside of uterus).
It may be difficult to pick up baby’s heartbeat with Doppler when the pregnancy is less than 14 weeks as before this gestation, the uterus is entirely within the pelvis.
How an Ultrasound is Done
An ultrasound is performed using an ultrasound probe or transducer that emits sound waves which are reflected back onto the transducer when the waves hit tissues within the body. The reflected echoes are then converted into signals by a computer system and visualised on a monitor as images.
In a transvaginal (internal) ultrasound, a small, long, wand-like transducer is used. It is first sheathed with a sterile condom and coated with sterile lubricant before it is inserted directly into the vagina. The doctor then moves the wand within the vaginal cavity to scan the uterus. This allows him to see the fetus even before it is detectable on a transabdominal ultrasound.
For a transabdominal ultrasound, gel is first applied to the surface of the abdomen before the doctor rolls the transducer over and around the abdomen. The gel helps to facilitate the transmission of sound waves which bounce off ‘structures’ to produce an image you can view on a video screen.
What the Ultrasound Reveals
Performed at around 20 weeks of pregnancy, a detailed anatomy scan is done to check that the baby has developed normally. In addition to checking that the appearances of various structures such as heart, kidneys and brain are normal, measurements of some of these structures are taken. The ease of completing this scan is influenced by factors such as the position of the baby inside the uterus, the maternal habitus, the presence of uterine fibroids, the presence of scar from previous caesarean section and the sophistication of the scan machine. The sonographer who does a detailed anatomy scan is someone who has been trained to competently perform this type of scan.
This is one of the most comprehensive and important screening tests carried out during your pregnancy as it tells you a lot about your baby.
For a quick glance, here’s a list of what ultrasound can reveal:
Preparing for an Ultrasound
There is no preparation required. However, before the test, your doctor may require you to drink two to three glasses of water and tell you to refrain from urinating so that your bladder will be full during the procedure. A full bladder is ideal as it will help the doctor view the baby better. There may be a slight discomfort from pressure on the full bladder, but otherwise, the ultrasound is absolutely painless.
2D, 3D and 4D Ultrasound Images
The sonogram that you usually get is the standard two-dimensional (2D) image. But newer imaging technologies are now available producing 3D or 4D images.
For those of you who are not familiar with the terms 2D, 3D and 4D, the 2D ultrasound which produces outlines and flat looking images can be used to see the internal organs of the baby because the scan sees right through your baby.
3D images, which look very much like the photos you see in newspapers and magazines, are used to show you three-dimensional external images which may be helpful in diagnosing problems such as a cleft lip. What 4D ultrasound brings to the table is that as the image is continuously updated, it becomes a moving image, like a movie. If you decide to have a 4D scan, you may be given a recording of it on DVD.
Edited by Dr Lim May Li, consultant obstetrician and gynaecologist from Gynecology Consultants Clinic & Surgery