Nobody knows what a normal amount of time is for third stage, because nearly all third stages today are actively managed (except for the few that happen too quick for that.) I would hesitate to call a placenta that took an hour or more to be born a "stubborn" placenta -- that implies that it was not normal. 
It does seem that among UCers placents do *not* tend to come out in the amount of time ACOG deems "normal" -- about 15 minutes -- the average seems to be closer to around an hour.
I know the concerns -- that the cervix will close up, or that the mother will be hemorrhaging and no one will know it. As for the first concern, it's highly unlikely that a healthy body allowed ideal circumstances in which to function would not be able to work out the the hormonal balance necessary to cue different parts of the body to do the right job at the right time. In short, in a body functioning normally, it's illogical that the cervix would begin to close up before the placenta is expelled. I would rather risk having to go the hospital than allow active management of my third stage -- because problems due to the latter are so much more likely than *naturally* occuring complications.
As for the second concern -- that the mother will be hemorrhaging and no one will know it because the placenta is preventing the blood from exiting -- the mother's demeanor is as good a clue as any as to what is going on inside her body. It's not like she's going to be laughing and rosy one minute and crash the next, you know? There are signs. To me, it's sufficient to be aware, eat the placenta if necessary (or just eat it anyway) and be prepared to transport; and the best prevention is to have a healthy mother who feels safe and supported, and an uninterfered-with birth. Until many more mothers are birthing in this way, we won't know how common hemorrhaging actually is in the natural world, but I suspect it would be very rare.
It does seem that among UCers placents do *not* tend to come out in the amount of time ACOG deems "normal" -- about 15 minutes -- the average seems to be closer to around an hour.I know the concerns -- that the cervix will close up, or that the mother will be hemorrhaging and no one will know it. As for the first concern, it's highly unlikely that a healthy body allowed ideal circumstances in which to function would not be able to work out the the hormonal balance necessary to cue different parts of the body to do the right job at the right time. In short, in a body functioning normally, it's illogical that the cervix would begin to close up before the placenta is expelled. I would rather risk having to go the hospital than allow active management of my third stage -- because problems due to the latter are so much more likely than *naturally* occuring complications.
As for the second concern -- that the mother will be hemorrhaging and no one will know it because the placenta is preventing the blood from exiting -- the mother's demeanor is as good a clue as any as to what is going on inside her body. It's not like she's going to be laughing and rosy one minute and crash the next, you know? There are signs. To me, it's sufficient to be aware, eat the placenta if necessary (or just eat it anyway) and be prepared to transport; and the best prevention is to have a healthy mother who feels safe and supported, and an uninterfered-with birth. Until many more mothers are birthing in this way, we won't know how common hemorrhaging actually is in the natural world, but I suspect it would be very rare.
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