Ultrasound for dating pregnancy
During your first trimester, you may have an early scan at about six weeks or seven weeks.
However, you'll only be offered an early scan if you're experiencing problems, such as pain or vaginal bleeding.
If you consent, you may also be scanned by someone who is training in ultrasound, under the direct supervision of a qualified sonographer. You can change your mind and withdraw your permission at any time.
Most of the time, the placenta has moved into a better position by the time you're 32 weeks pregnant.
This is because the sound waves go through them with no echoes.
The person performing the scan (sonographer) will look at these different shades to interpret the images.
An ultrasound scan sends sound waves through your womb (uterus). The echoes are then turned into an image on a screen that shows your baby’s position and movements.
Hard tissues, such as bone, reflect the most sound waves and so make the biggest echoes.