Overview of Obstetric Ultrasound
Doctors first used ultrasound technology to detect early pregnancies in the womb during the 1960s and 70s. By the 90s, emergency medical professionals began using this technology at the point of care, or when and where treatment is given. Using ultrasound, which is a harmless and non-invasive diagnostic tool, doctors are now able to confirm a pregnancy on the spot. This has helped to reduce waiting times for pregnant patients in emergency departments.
Pelvic ultrasound, conducted by emergency medical providers, is most effective in diagnosing conditions during the first three months of pregnancy. Therefore, the use of ultrasound in early pregnancy has become a major focus of discussion and study.
Anatomy and Physiology of Obstetric Ultrasound
The uterus, which is an important part of the female reproductive system, has two main landmarks – the bladder and the vaginal stripe. The bladder is positioned in front of and below the uterus, while the vaginal stripe is a bright, reflective line that’s found behind the bladder. The vaginal stripe extends up to the cervix. Usually, the top part of the uterus, known as the uterine fundus, curves forward (this is the case in about 80% of women) but in some women, it curves backward. The endometrium, which is the lining of the uterus, typically appears as a bright line in the center of the uterine fundus.
An ultrasound can confirm if a woman is pregnant by detecting a gestational sac within the uterus. This sac should contain a yolk sac and/or demonstrate a fetal heart rate. Additionally, the ultrasound should show a lining of a particular thickness around the baby’s prospective home in the uterus. If these features are missing, a definite pregnancy cannot be confirmed.
Why do People Need Obstetric Ultrasound
If a woman in her early stages of pregnancy is experiencing vaginal bleeding, it is crucial to confirm whether the pregnancy is occurring inside the uterus, referred to as an “intrauterine pregnancy” or IUP. If the pregnancy is inside the womb and accompanied by vaginal bleeding, it rules out a possibility of an “ectopic pregnancy,” – a condition where the fetus grows outside the uterus. Under such conditions, the risk faced is usually a “threatened abortion” or potential miscarriage. However, if it’s not an IUP and there’s vaginal bleeding, you should get checked for an ectopic pregnancy.
It’s common for emergency physicians to be the first people to perform an ultrasound in the early stages of pregnancy. This is because most obstetricians (doctors who look after you during pregnancy) schedule the first appointment around 8 weeks from the last menstrual period. If you have taken a home pregnancy test and it’s positive, you might go to an Emergency Department to confirm the pregnancy, even if you don’t have any symptoms. Here, an ultrasound is used to not only confirm whether it’s an IUP but also to determine the age of the fetus. In an instance where the ultrasound doesn’t detect an IUP in an asymptomatic patient, a hormone test called “beta-hCG” should be ordered. This test needs to be repeated after 48 hours to check if the hormone level is rising as expected.
If you’re experiencing abdominal pain during early pregnancy, an IUP confirmation can rule out an ectopic pregnancy, provided you didn’t conceive through reproductive assistance. However, If an ectopic pregnancy is found – where there’s a fetal heartbeat or yolk sac outside the uterus – immediate medical help should be sought for surgical intervention.
In cases where an IUP is not found, and there’s fluid in the lower part of your abdomen or pelvic area, it may indicate an ectopic pregnancy that requires surgical intervention, especially if you’re experiencing severe abdominal pain and signs of low blood pressure.
Excessive nausea and vomiting (“hyperemesis gravidarum”) during pregnancy can be indicative of twin pregnancies or a molar pregnancy (a condition in which tissue that normally becomes a fetus instead becomes a growth in the uterus).
If the ultrasound carried out externally on your lower stomach doesn’t show an IUP, you will then need a transvaginal ultrasound. This is a type of ultrasound where a special probe is inserted into the vagina to give a clearer picture. And if you had reproductive assistance to get pregnant, reach out to your specialist for further advice.
When a Person Should Avoid Obstetric Ultrasound
There are no strict reasons that would prevent a doctor from performing a type of ultrasound called a ‘transabdominal pelvic ultrasound’ in early pregnancy. This means placing the ultrasound device on the belly to view the baby in the womb. However, doctors should avoid scanning over any cuts or surgical wounds so as to avoid causing any infection.
An internal type of ultrasound that’s called a ‘transvaginal ultrasound’ may not be safe if a woman has low blood pressure, or ‘hypotension’. This is a situation where it’s not safe to perform the test.
Furthermore, it is recommended to use the lowest possible ultrasound settings that are still able to get a clear image of the baby during the first three months of pregnancy. This is a practice known as limiting to ‘as low as reasonably achievable’ (ALARA) frequencies. To adhere to this, doctors avoid using certain features of the ultrasound machine like color and spectral Doppler during the examination.
Equipment used for Obstetric Ultrasound
If a pregnant woman needs an ultrasound in the first three months of her pregnancy, she should have it done using a special type of ultrasound machine. This machine uses a low-frequency probe, which is a tool that sends out sound waves to create images of the baby. Ideally, this probe should have a large curved or “convex” surface.
There may be times where a different kind of ultrasound, called a transvaginal ultrasound, is recommended. This involves using a special probe that can be inserted into the vagina. This probe is usually covered with a protective sheath and can provide a better view of the uterus and nearby structures.
It’s crucial to keep the vaginal probe clean to prevent infection. A high-level disinfectant system is used between each use for this purpose.
Who is needed to perform Obstetric Ultrasound?
A healthcare professional who has had proper training can carry out an ultrasound scan during the first three months of pregnancy. Emergency doctors are required to be able to do and understand a minimum of 25 to 50 heart ultrasound tests by the time they finish their training. An ultrasound scan uses sound waves to create images, this helps doctors to see and monitor a pregnancy or to check the heart.
Preparing for Obstetric Ultrasound
During a pelvic ultrasound through the abdomen (transabdominal), it is best if the patient’s bladder is full. This is because a full bladder creates a clearer picture of the uterus on the ultrasound screen, much like a window you can see through. The patient will be asked to lie flat on their back on a stretcher. Their stomach will need to be uncovered and towels will be tucked around their clothing to protect them from the ultrasound gel. If the person operating the ultrasound machine is right-handed, the machine should ideally be placed on the patient’s right side. The machine will need to be switched on and connected to power. If possible, the room lights will be dimmed to make the screen easier to see.
It’s important to have a transabdominal pelvic ultrasound before a transvaginal ultrasound. That’s because they provide different kinds of information to doctors. Before performing a transvaginal ultrasound, the patient’s bladder should be as empty as possible. This makes it easier for the ultrasound ‘wand’ or probe to get closer to the uterus and the adnexa (the structures around the uterus). To get a good view of a uterus that is tilted forward (an anteverted uterus), the patient should be positioned on a stretcher with supports for their legs (stirrups). The patient’s pelvis should be at the edge of the stretcher. Alternatively, their pelvis can be elevated around 8 to 10 cm, using an upside-down bedpan and a few folded-up disposable pads called chucks.
How is Obstetric Ultrasound performed
When performing a pelvic ultrasound, medical professionals use a special device called a low-frequency convex probe. This device is placed just above the patient’s public area to examine the pelvic region in detail. In case this type of probe isn’t available, an alternative device known as a phased array probe can be used. To get the best results, the ultrasound machine is typically set to “obstetrics” or “pregnancy.”
The ultrasound captures an inner view of your body in a sagittal (vertical) view through the uterus. The technician puts the probe just above the public bone, aiming it upward. Images of different structures or organs appear on the ultrasound screen. Structures closer to the probe appear at the top of the screen, and structures further away appear at the bottom of the screen. This means the top of the screen is showing the front portion of your body (anterior), and the bottom of the screen is showing the back portion of your body (posterior).
If your bladder is full during this scan, it will mostly occupy the top part of the ultrasound screen. Just behind the bladder, a sonographer will identify a line leading towards the cervix and uterus, known as the vaginal stripe. This process allows the healthcare professional to create a complete view of the uterus and confirm the presence of a pregnancy inside the uterus (intrauterine pregnancy or IUP). If a baby’s heartbeat is detected, they will use a special feature called the “Motion-Mode” to calculate the baby’s heart rate.
In some cases, a transvaginal ultrasound may be required – this involves using a high-frequency probe. The probe, which looks like a rifle, is inserted into the vagina with the indicator pointing upwards (towards the ceiling). The ultrasound images will then provide an internal view of the uterus from a different angle and provide more detail, allowing the healthcare provider to see any abnormalities or pregnancies.
The ultrasound probe is then rotated counterclockwise by 90 degrees to provide a transverse view of the uterus. This view enables the technician to locate the cornua, where the uterus narrows on either side, and the fallopian tubes originate. The ovaries are usually located between the cornua and the adjacent iliac vessels, and they may be identified during the ultrasound process.
Overall, these ultrasound methods help detect and analyze pregnancies and other conditions in women. The professional would guide the process, ensuring a smooth and comprehensive examination of the woman’s reproductive system.
Possible Complications of Obstetric Ultrasound
Having a pelvic ultrasound is generally safe and poses little to no risk. It’s a diagnostic tool that doctors use to see inside your pelvis. During this procedure, there might be some slight discomfort when the ultrasound probe is pressed against your abdominal area, whether it’s on the outside (transabdominal) or inserted into the vagina (transvaginal).
What Else Should I Know About Obstetric Ultrasound?
A pelvic ultrasound is a quick, affordable and safe procedure that can quickly determine if a woman is pregnant. This tool becomes especially crucial when there is a possibility of a dangerous condition such as a ruptured ectopic pregnancy – when the pregnancy develops outside the womb. In such cases, the ultrasound can detect any fluid leakage or non-detected intrauterine pregnancy, which can help in providing timely medical care.
