Spoke to my midwife, they will not do another us unless it is an emergency because they are a busy unit and by the time i'll get an appointment it will be time for my 20 week scan anyway.
She is a little concerned at the size of my uterus because its 5cm more than what she would expect, and the fact the heartbeats are independently moving and feeling movements, i have my next appointment in 2 weeks and she quite happy to wait till then to see me as my health hasn't been affected and no strange pains/bleeding etc.
At 12 weeks they would have seen the other baby but you can always request another sonogram. Def could be your placenta and also on my home doppler, depending on where I hold the wand it can register 2 different range of beats at different areas.
Could always request another ultrasound, too make sure. At 12 weeks. The babies are pretty visible, but stranger things have happened
The sonographer did say that placenta was to the right, both heartbeats are to the left. The lower one i have wand thing pointed towards my back, the higher one the wand thingy angled up towards belly button. And they sound identical, coming through the placenta there should be a kind of whooshing sound with it.
Could be your placenta if it is anterior. I had the same but the doctor can say which one is what...
They likely would've seen a second baby on a 12 week ultrasound.