Comparing Internal and External Ultrasound Scans

When you have a scan, it can be performed either internally or externally. Both kinds of scan work in the same way, using equipment that converts sound waves into pictures. Whether you have a transvaginal (internal) or abdominal (external) scan depends on what it’s for, and other factors.

Reasons for Scans

In general, women have internal scans earlier in a pregnancy and external scans later on in a pregnancy.

The reason for this is that in an internal scan the probe is closer to the uterus and can produce better quality images. This means an internal scan can detect a developing baby much earlier than an external scan, so an internal scan is often performed to detect a pregnancy in the very early stages.

Abdominal scans are performed once the baby is large enough for abdominal scans to produce clear images. For instance, the Nuchal Translucency Scan, performed at 12 to 14 weeks, is an external scan. From this point in a pregnancy, internal scans are usually only performed if an external scan can’t produce a clear image.

Preparing for the Scan

For both scan types, there’s very little preparation that you need to do. Typically, the only factor you need to worry about beforehand is whether your bladder is full or empty. If there are any other instructions, we’ll let you know before your appointment.

For an external scan your bladder usually needs to be full. The Birth Company recommends drinking some water on arrival.

For an internal scan it is best if your bladder is empty. You’ll be able to do this at The Birth Company, just before your scan.

Scan Method

In an external scan the scan probe is placed against your abdominal skin. You’ll need to remove or adjust any clothing items that cover up your abdominal area, so that the skin is sufficiently exposed.

In an internal scan the probe is gently inserted into your vagina. The probe used here is specially designed to be as comfortable as possible. You’ll need to remove the clothing from your lower body and will be given a cover during the scan.

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137 Harley Street, London W1G 6BF
Nearest Underground Tube Stations

Baker Street
Regent’s Park
Great Portland Street


Talbot Road, Talbot Road, Alderley Edge, Cheshire SK9 7HR
Nearest Overground Train Station

Alderley Edge