If you're between 26 weeks and 30 weeks pregnant then this is the best time to have a 3D or 4D scan. Before that baby has very little fat under her skin. It's natural that you'd like to see your baby's face on the scan and enjoy your pregnancy.
All medical procedures have risk. Some doctors like to do 3D & 4D ultrasounds because certain birth defects, such as cleft palate, that might not show up on a regular ultrasound. So, 3D and 4D ultrasound exams allow you to see your unborn baby in even more depth and detail than a standard 2D ultrasound.