Pregnancy Scans: Internal vs. External

Understanding Pregnancy Scans: Internal vs. External Approaches

Navigating the journey of pregnancy often involves various medical appointments, and among the most significant are ultrasound scans. These scans are invaluable tools for monitoring the development of your baby and ensuring a healthy pregnancy. However, you might hear terms like 'internal scan' and 'external scan' and wonder about the distinctions. This article aims to demystify these two common methods, explaining why and when each is typically employed, and what you can expect in terms of preparation and the procedure itself.

The Core Differences: Proximity and Image Clarity

The fundamental difference between an internal and an external scan lies in the placement of the ultrasound probe and, consequently, the clarity and timing of the images produced. In essence, it's about how close the technology gets to the developing baby.

Internal Scans: Early Insights

Internal scans, often referred to as transvaginal ultrasounds, involve a specially designed, slender probe being gently inserted into the vagina. This method allows the probe to be positioned very close to the uterus. Why is this proximity so crucial? Because it enables the ultrasound waves to travel a shorter distance, resulting in higher-resolution, more detailed images, especially in the very early stages of pregnancy. This enhanced clarity means that an internal scan can detect the presence of a developing pregnancy, and even early fetal structures, much sooner than an external scan. Consequently, internal scans are frequently the go-to method for confirming a pregnancy in its initial weeks, typically before 8 weeks gestation.

External Scans: A Broader View

External scans, also known as abdominal ultrasounds, involve the ultrasound probe being placed on the surface of the abdomen. A gel is applied to the skin to ensure good contact and to help the sound waves travel efficiently. For this type of scan to produce clear images, the baby needs to have developed sufficiently to be visualized through the abdominal wall. As the pregnancy progresses and the uterus grows larger, the baby becomes more accessible for external imaging. This is why external scans become more common as the pregnancy advances. A prime example is the Nuchal Translucency (NT) scan, usually performed between 12 and 14 weeks of pregnancy, which is an external procedure.

Reasons for Choosing a Specific Scan Type

The choice between an internal and external scan is primarily dictated by the gestational age of the pregnancy and the specific information required by your healthcare provider.

Early Pregnancy Detection

As mentioned, internal scans excel in the early stages. They are instrumental in:

• Confirming an intrauterine pregnancy.
• Assessing the viability of the pregnancy (detecting a heartbeat).
• Identifying the number of fetuses (e.g., twins).
• Evaluating early fetal development and dating the pregnancy accurately.
• Investigating potential issues like ectopic pregnancies or early signs of miscarriage.

Mid to Late Pregnancy Monitoring

Once the pregnancy is well-established and the fetus has grown larger, external scans become the preferred method. They are used for:

• Monitoring fetal growth and development.
• Assessing the baby's position and presentation (e.g., head down or breech).
• Checking the placenta's position and health.
• Measuring amniotic fluid levels.
• Detailed anatomical surveys to check for abnormalities.
• The Nuchal Translucency scan at 12-14 weeks.

It's important to note that even in later pregnancy, if an external scan doesn't provide a clear enough view of a particular area, an internal scan might still be employed, though this is less common.

Preparing for Your Scan: What to Expect

Generally, preparation for both types of scans is minimal, but there are a few key differences to be aware of, primarily concerning bladder fullness.

Preparation for External Scans

For an external abdominal ultrasound, a full bladder is often recommended. A full bladder acts as an acoustic window, pushing the bowel out of the way and providing a clearer view of the uterus and the developing baby. Healthcare providers will usually advise you to drink a specific amount of water (often around 1-2 pints or 500-1000ml) about an hour before your appointment and to avoid emptying your bladder. You may be asked to stay hydrated leading up to the scan.

Preparation for Internal Scans

Conversely, for an internal (transvaginal) scan, an empty bladder is preferred. A full bladder can actually obstruct the view during this procedure. Therefore, you will typically be advised to empty your bladder just before the scan. You will usually be offered a private space to do this.

In both cases, your healthcare provider will provide specific instructions beforehand. If you are unsure about any aspect of the preparation, don't hesitate to ask.

The Scan Procedure: Step-by-Step

Understanding the process can help alleviate any anxiety you might have.

What Happens During an External Scan?

During an external scan:

1. You will be asked to lie down on an examination couch, usually with your abdomen exposed. You might be given a sheet or gown to cover the parts of your body not being scanned.
2. A clear, water-based gel will be applied to your abdomen. This gel is essential for transmitting the ultrasound waves.
3. The sonographer (the person performing the scan) will then place the ultrasound probe on your abdomen and move it around to capture different views.
4. You may be asked to hold your breath at certain times to get a clearer image.
5. The sonographer will explain what they are seeing and may show you images on the screen.
6. After the scan, the gel will be wiped away, and you can get dressed.

What Happens During an Internal Scan?

During an internal scan:

1. You will be asked to undress from the waist down and lie on the examination couch, usually with your feet in stirrups, similar to a gynaecological examination.
2. You will be given a cover or sheet to maintain your privacy.
3. The sonographer will use a sterile, disposable cover over the ultrasound probe, similar to a condom, and may apply a small amount of lubricant.
4. The probe will be gently inserted a short distance into the vagina. You should not feel significant discomfort, though some mild pressure is normal.
5. The sonographer will move the probe to obtain specific views of the uterus, ovaries, and early pregnancy.
6. You can usually ask the sonographer to stop at any time if you feel uncomfortable.
7. After the scan, the probe is removed, and you can get dressed.

Key Takeaways: A Comparative Glance

To summarise the main distinctions, consider this comparison:

Frequently Asked Questions

Q1: Is an internal scan painful?

Most women do not find internal scans painful. You might feel some mild pressure as the probe is inserted and moved. If you experience any significant discomfort, it's important to let the sonographer know immediately. The probes are designed to be as comfortable as possible.

Q2: Will I need an internal scan if I'm having twins?

Whether you need an internal scan depends on the stage of your pregnancy and the specific information required, regardless of whether you are carrying one baby or multiples. Internal scans are often used in early twin pregnancies to confirm the number of sacs and fetuses.

Q3: Can an external scan detect a miscarriage?

External scans can help identify signs of miscarriage, such as a lack of fetal heartbeat or an empty gestational sac. However, in very early pregnancy, an internal scan may be more definitive due to its superior image quality at that stage.

Q4: How soon can a heartbeat be detected?

A fetal heartbeat can often be detected via a transvaginal (internal) ultrasound as early as 6 weeks of pregnancy. It may be visible on an abdominal (external) scan a week or two later.

Q5: What if I'm too embarrassed for an internal scan?

It's completely normal to feel a bit apprehensive or embarrassed. Remember that the sonographer is a medical professional who performs these scans routinely. They are trained to be discreet and professional. You will be given privacy to undress and a cover during the procedure. If you have significant concerns, discuss them with your healthcare provider before the appointment.

Conclusion: Informed Choices for a Healthy Pregnancy

Understanding the differences between internal and external scans empowers you to be an active participant in your prenatal care. Both methods are safe, non-invasive (apart from the probe insertion in internal scans), and provide crucial information about your baby's development. Your healthcare provider will always choose the most appropriate method based on your individual circumstances and the stage of your pregnancy. By knowing what to expect, you can approach your scan appointments with confidence, knowing that these diagnostic tools are there to ensure the best possible outcome for you and your growing baby.

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