I've seen about a dozen true knots, none have been in babies with any problems. They have mostly been picked up while I'm checking out the placenta, just one of those things.
Velamentous insertions however, now they make me nervous. Had a scary one years ago when the mum rang to say her waters had broken and they were green. Got her to come straight into the facility I was already in , fetal heart in it's boots, straight off the theatre. The cord was a true velamentous insertion with loops of cord on the fetal side, just hanging loose in the fluid. Absolute miracle that baby didn't catch one while moving around. Still gives me the willies, but a true knot, phef, not such a big deal.
I agree with the poster who commented that funky fetal heart would make me think cord involovement/compression, but not true knot.
Have had a mum lose a baby due to chrionic bands wrapping around the cord and all but cutting it. Rather like band amputations of fingers and limbs. poor wee bub