Dating scan nuchal translucency
You may know when your LMP was, but not when you actually conceived.
A blood test at what you thought was 13 weeks wouldn't be helpful if you were actually 16 weeks pregnant.
Keep it with your maternity notes so your midwife and anyone else involved in your care can see it. This measurement, known as the crown rump length (CRL), is very accurate in the first trimester.
How big your baby will be depends on when you have the scan: After 13 weeks, your baby can curl up and stretch out, so measuring the length becomes less accurate.
If your womb (uterus) is very deep in your pelvis, or if you're overweight, you may be offered a vaginal scan, which can get a closer view of your baby.
It shouldn't be uncomfortable, and you don't need a full bladder Your sonographer will give you a report of the scan, which will tell you exactly how many weeks pregnant you are.The test results in providing a 90-95% accuracy rate and can help you decide whether or not to have further diagnostic tests.