In normal state, each body tissue type, such as liver, spleen or kidney, has a unique echogenicity.Fortunately, gestational sac, yolk sac and embryo are surrounded by hyperechoic (brighter) body tissues.An image of your fetus will appear on an accompanying computer screen and while looking at this image, the technician will take some standard measurements from different angles and listen for a heartbeat.
If you can't remember your last menstrual period date or if you have consistently irregular cycles, the doctor can use an early ultrasound to give you a fairly reliable due date.
Research shows that routine obstetric ultrasound before 24 weeks gestational age can significantly reduce the risk of failing to recognize multiple gestations and can improve pregnancy dating to reduce the risk of labor induction for post-dates pregnancy.
There is no difference, however, in perinatal death or poor outcomes for babies.
If your first ultrasound gives you a due date that is more than 1.2 weeks away from what was expected, there is a good chance that everything is still fine.
You may have simply conceived earlier or later than you thought you did (which can happen if your cycle is at all irregular or if you remembered your last menstrual period date incorrectly).