Dating Ultrasound is performed in order to establish the gestational age and reveal important information of the fetus. The earlier a dating ultrasound is done, the more accurate it is at estimating the baby’s due date. Studies shows that Ultrasound 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. This is because the fetus is growing so quickly that there is a big difference in size from week to week. Also the fetus cannot bend and twist too much yet, so the length of the body is fairly constant.