I think that it is good to understand that the placenta can take it's time to come away. Before my DD was born, and we were at antinatal classes (both NCT and community hospital), the timings for the 3rd stage were given to us as; 15min for a managed 3 stage and physiological about 30 to 45 min. However, this isn't always the case! Mine took just under 2 hours to come away.. and no one was worried. I would be perfectly happy to wait this amount of time again.
The plusing of our cord took about 20-30min to stop with us.
It is stimulated both by baby and mother. In the first instance by the baby taking it's first breaths - as the babies circulation rapidly has to change from circulating to the cord and the placenta for oxygen, to the plumonary lung circulation. Cutting the babies blood flow just inside babies belly button as the redirection to lung circulation is very very important. Second action to stop pulsation, is the hormonal changes within the mother, as the placental circulation is contracted with oxytocin produced with in the mothers brain. The tissues restrict, initiating the disconnection of the placenta, and the sitimulation of the uterus to contract and deliver the placenta.
So baby will rapidly NOT be receiving any blood from the placenta upon taking first breaths. (even though the blood within the cord is babies blood not the mother's - the oxygen and neutrient exchange point is in the placenta) The remaining plusing of the cord comes from the placental circulation from the mother to the cord, and won't stop until the placental connection has been restricted.
However both stages of this can be delayed.. so until babies breathing is established, and not taking cord blood, there isn't the negative feedback needed (of the blood not circulating t baby) to stimulate the constriction on the uterus at the site of the placenta. It is all very interconnected! I would never, never want to have cord cut before babies breathing was established!! In fact DD was born in water, so it was essential for her to come up for air first - as she was still getting all her needs from me, until those first few breaths, she didn't really know she was born! This in my mind is similar to being on land, and cutting the cord immediatly without established breathing - It is akin to baby suffocating. (not to be too dramatic!)
So in summary, it is better for the mother and baby if cord is allowed to stop circulating blood to baby, before clamping or cutting (if you need to cut at all)
I don't want (and didn't with my first) to have the cord cut at all. Though I have to say, that we did have a cord cut after 30mins with DD as I needed to walk about, as I had the most painful cramp in my whole leg that I have ever experianced!!! Cest la vie!
xXx