It is dependant on what doppler you have. Some work from 10-12 weeks onwards, others from 16 weeks and then some from 20+ weeks.
The swooshing sounds like the blood flow through the placenta or perhaps your own arteries. Babys heartbeat should sound like a train thudding by, or a horse galloping. As stomp said, it would sound like a very fast heartbeat almost twice as fast as your own.
That happened to me before, i was struggling to find it a bit then hubby made me laugh and I lost it.
I am sure I can hear bubba moving about as it sounds like something moving in water. It is very possible that baby has moved a bit and that's why you can't find it, they are good at hiding!!
Try not to stress yourself out. Easier said than done I know but it won't do you any good. Just chill leave it and try again this evening.
As the others have said, it will sound very fast like a train or horse galloping and i too now often hear it mixed with the water sound.
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