best dating website for professionals - First trimester dating ultrasound accuracy
You probably know when your LMP was, but not when you actually conceived.
If you are having a screening test for Down syndrome, you'll be offered a dating scan first.
The test needs an accurate due date to be reliable, as hormones in your blood vary according to your stage of pregnancy.
After 13 weeks your baby can curl up and stretch out, so measuring the length becomes less accurate.
Then the circumference of the head becomes the best way to measure your baby Some hospitals and private clinics offer a dating and screening scan at the same time.
Nearly all scans after 10 weeks can be done through your tummy, and most units ask you to come with a full bladder.