My OB and the midwives I've seen all say a bubs heartrate should vary btn 110-160 and not remain the same like an adults so I'm not sure how this theory is supposed to work. I've had 3 CTGs in the last week so have seen this variation in action a lot and it's not always related to movement or BHs. Maybe it's like those chinese lunar charts - it works for some but not for others. Fun to speculate though!