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.
Does ultrasound tell fetal age or gestational age?
During an ultrasound, your doctor will measure your babys head and your abdomen to determine gestational age. After birth, gestational age is determined using the Ballard Scale, which assesses the physical maturity of your baby. Gestational age is divided into two periods: embryonic and fetal.
How can an ultrasound tell the age of a fetus?
One of the biggest benefits of an ultrasound is that it can estimate how far along you are in your pregnancy (gestational age) down to just a few days. Ultrasounds estimate how far along you are in your pregnancy by comparing the growth of the fetus to established growth rates for babies around the world.
Do you add 2 weeks to gestational age in ultrasounds?
An ultrasound is actually the most accurate way to date a pregnancy because all fetuses grow at a consistent rate during the first trimester and early second. In other words, if your baby measures 9 weeks 2 days when you have your ultrasound, thats how far along you are, no matter when your last period was.
How accurate is gestational age?
The earlier the ultrasound is done, the more accurate it is at estimating the babys due date. Ultrasounds performed during the first 12 weeks of pregnancy are generally within 3 - 5 days of accuracy. The most accurate time is between 8 and 11 weeks gestation.