Accuracy of ultrasounds for dating

The LMP is used because most women know when their last period was, but may not know when they actually conceived.If you do know the conception date, this is classed as day 14 and not day one.

He used a condom, I believe I was on birth control (but cant remember for sure), and took Plan B 55 hours later.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.Transvaginal ultrasound is safe and commonly performed during all stages of pregnancy, including the first trimester. Transabdominal ultrasound involves scanning through your lower abdomen.A small amount of ultrasound gel is put on the skin of the lower abdomen, with the ultrasound probe then scanning through this gel.