My first midwife had me pushing at 15 minutes after the birth! ARGH! My second we waited an hour and fifteen minutes. The midwife was starting to get antsy even though I was feeling and looking great
so for her benefit I got up into a squat and it came out shortly thereafter. (Thinking back on it, geez I really
didn't need all those people there waiting and staring and... ugh.)
When the placenta separates there may be a lengthening of the cord, and a gush of blood. I haven't noticed that myself. I think more telling is the change in mood of the mother. Your focus will spontaneously shift from the baby back to your body, and you sort of "wake up" a little bit. It's a subtle thing, I think you might not notice if a lot was going on. With my last UC, I think I know right when my placenta separated. I was completely focused on the baby in this kind of timeless space, then about 10-15 minutes after the birth I naturally drifted out of that birth consciousness, I became more aware of what was going on around me, and I started gettting uncomfortable. (I think that's when it happened.) I got up then and walked to the living room (other side of the house) and sat in the recliner. After a while (another 10-15 minutes ) I started feeling kind of antsy, like I was ready to do something, and I handed the baby to my husband and squatted over a bowl. At first it seemed "stuck" -- nothing seemed to be happening. Then I got that strange feeling, sort of a prickliness and pressure and feeling of fullness, and out it came.
I have never had pieces detach, but looking at the placenta it seemed pretty obvious to me that I would know if a piece was missing. It had a smooth surface, like covered by a thin layer of gelatin, and was the same everwhere (on each side, of course, as they are different.) What I was less clear on was if the membrane was whole. It's stretchy and clingy and thin and hard to examine. (I thought.) My uterus was firming up and I felt fine, though, so I didn't bother much about it.