Ultrasound measurement of the embryo or fetus in the first trimester (up to and including 13 6/7 weeks of gestation) is the most accurate method to establish or confirm gestational age.

How can pregnancies be dated?

The most common way to calculate your due date is to start with the first day of your last menstrual period (LMP). Add 7 days, and then count backward 3 months. For example, if your last period started on March 20, you would add 7 days to get March 27. Then subtract 3 months to get a due date of December 27.

Which is more accurate LMP or ultrasound?

When ultrasound was used instead of certain LMP, the number of postterm pregnancies decreased from 10.3% to 2.7% (P <. 001). Conclusion: Ultrasound was more accurate than LMP in dating, and when it was used the number of postterm pregnancies decreased.

When do you use corrected age?

There isnt a set age when you should stop correcting a childs age for prematurity. But most health professionals recommend correcting at least until your child is two years old.