The switch up

Today I went into my RE for my second ultrasound. Well it turns out that this week they are telling me that baby A is now baby B and they just flip flopped. Okay so does that mean that there is 1 or 2 in there? Well it still looks like I have 2 sacs. They were able to identify one sac with a baby with a heartbeat of 154bpm. The other sac they were having difficulties seeing because of the shape of my uterus and the location of the sacs. So now they want me to come back in 2 weeks and hopefully we should have the final verdict but my guess is it is probably a singleton pregnancy.