The Ultrasound Scan


Private Care & Tests During Pregnancy, in London & UK »

Part of modern antenatal care (any and all medical care or treatment administered during a pregnancy) is regular testing and screening to ensure that both mother and child are healthy. Fortunately we now have access to many safe and effective means of keeping an eye on the progress of pregnancies, and of these the ultrasound scan, also known as the sonogram, is an invaluable tool.

Why are ultrasound scans performed during pregnancies?

An ultrasound scan (or sonogram) is an easy to use, effective, and above all safe method of visualising a developing unborn embryo or foetus. As the progress of human pregnancies is well understood, ultrasound scans are performed throughout the 9 months of the average pregnancy to make sure that everything is going as it should.

An ultrasound scan can be used to monitor the overall growth of a foetus, as well as to look for particular changes

How does an ultrasound scan work?

An ultrasound is much safer than alternative imaging technologies like X-Rays or MRIs as no radiation is used. As a foetus is particularly vulnerable to the effects of radiation, these other options are not really applicable during a pregnancy.

Fortunately ultrasound images are just as, if not more, useful as radiation based alternatives, and are generated by means of inaudible sound waves (called ultrasound) which are both emitted and picked up by a probe (referred to as a transducer) designed to generate and detect ultrasound. The probe is placed on the womb and firsts generates ultrasound waves, these are reflected to different degrees by the different materials within the womb, the probe (and its attached computer) will then interpret this variation in signal as an image which can be seen and interpreted by a trained ultrasound technician.

This description is of the general form of ultrasound widely used in the NHS and in private medicine, which is also referred to as external ultrasound. There are alternative forms of ultrasounds which are used less often, usually if a standard ultrasound picks up something which your doctor might want to investigate further.

For example internal ultrasounds are used to better image particular organs and structures, and this type of ultrasound involves the insertion of the probe mentioned above into the female reproductive tract, which, as you can imagine, is not entirely comfortable and as such is avoided unless un-necessary.

An endoscopic ultrasound works on the same basic principle, but rather than the standard apparatus used for an ultrasound scan, an extremely fine, flexible tube is passed down the throat to examine the stomach for instance. This tube is referred to as an endoscope, and is broadly used in medicine for imaging purposes. Endoscopic ultrasounds are rarely used during a pregnancy, and if they are it is usually to investigate a recurring problem in the digestive tract.

When are ultrasound scans performed during a pregnancy?

Depending on whether this is your first pregnancy, and on whether you are receiving your antenatal care from the NHS or from a private provider. Generally speaking however, ultrasound scans are a regular feature of appointments throughout your antenatal care. Significant ultrasound scans include, for example, the early pregnancy scan, which is used to provide your first glimpse of the foetus. Similarly the scan performed during the second trimester is often significant as it indicates the sex of the foetus, and so marks a major point in the progress of a pregnancy.

Ultrasound scans are not only used to monitor foetal health, they are also an important tool in ensuring that a mother is doing well, and as such ultrasound scans will often be performed if you report anything particularly unusual that your midwife or doctor decides to look into.  

What is involved in an ultrasound scan?

As mentioned above, the standard external ultrasound scan basically involves applying the probe (aka transducer) to the surface of your belly, and letting the machinery do the rest. A cool gel is applied to your stomach prior to the scan. This substance is known as a coupling gel, and is essentially used to enhance the quality of the image produced.

For some kinds of ultrasound you may be told not to eat for a number of hours prior to the scan, or alternatively for you to drink plenty of liquids to fill up your bladder for the test. The latter is often suggested prior to pregnancy scans. If you aren’t given any instructions prior to your appointment, then there probably isn’t anything you need to do for it!

Are ultrasound scans safe?

As mentioned above, ultrasound scans are very safe because sound waves are used rather than radiation, which can cause genetic damage to an unborn baby, particularly during the early stages of a pregnancy when scans are needed.


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