Ultrasound not always shows. I had an ectopic pregnancy and the doc couldnt find it. Only blood test showed, so i had a surgery cause it was too late for medication. I first had lapharoscopy and thats how he realized that pregnancy is placed in a tube.
It shows very clearly. The liquid in the sac around the baby is very vivid on an ultrasound, and the position (not in the uterus) is also really obvious.