If you have an irregular cycle, or if you've recently been taking the contraceptive pill, working out the date from your LMP isn't a very accurate method.
Ultrasounds are more accurate than using the LMP and, if the ultrasound date differs from your period dates, the ultrasound date will be used.
This information is to help you with questions you may have. Ultrasound uses high frequency sound waves to see internal structures of the body.
An ultrasound examination obtains a picture of the inside of the body without the use of X-Rays.He/she may also write a letter explaining his/her concerns.