With my twins I didn't get an ultrasound until 20 weeks! I had one to be able to calculate my due date due to irregular periods (didn't concieve until Sept but hadn't I was 7 weeks it looked like a peanut but i saw and heard the heartbeat.
Pregnancy Due Date Calculator - Perinatology.com
1st trimester ultrasound how to, normal appearances, yolk sac, chorion, amnion, way to "date" an early pregnancy is to add the length of the fetus (in mm) to 6 weeks. but this will increase to between 120- 180 beats per minute by 7 weeks. Initially twins may be identified as 2 separate gestational sacs (ie diamniotic,
7 Week Ultrasound Question? - Circle of Moms