This happens during 18th - 20th week of pregnancy. At this time, you are half way your pregnancy and you really look pregnant.
Scan normally takes 20 to 40 mins and it can take longer if there are multiple fetus. At this stage fetus is developed and can be seen. At this stage growth of organs can be seen and much more detail can be obtained from images.
After the scan, doctor can actually tell the growth of child, count fingers and toes, check for any abnormalities in heart, brain, liver etc and much more. This scan gives clear picture of child's health **
You might even get a 3-D view, which will offer a true-to-life glimpse of your baby's nose and bone structure. **