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.
What is the best time to have an ultrasound?
The American College of Obstetricians and Gynecologists (ACOG) says that women should get at least one sonogram in the second trimester, between weeks 18 and 22 of pregnancy. You may also receive an additional ultrasound in the first trimester, before your 14th week of pregnancy.
How early can ultrasound detect?
In viable pregnancies, trans-vaginal (internal) scans should be able to detect a gestation sac from 5 weeks of pregnancy. A yolk sac can be seen at 5 1/2 weeks gestation. Trans-abdominal (external) scan may be less accurate at this early 5 week stage.