Well, folks, I hate to throw skunk in the bunkhouse, but I pasture-bred 5 mares to a son of Real Gun (AQHA Super Horse a few years back) and I don't have a clue which ones are in foal. They will tell me in a couple of months. I do not even know any breeding dates on any of them and they will all foal on pasture next spring. I bred 2 mares to my old horse, wrote down breeding dates but did not even check them back. I bred them pretty late and did not want them bred any later than that.
Last year I bred 7 mares total and I have 7 foals about ready to wean right now. All of them were bred on pasture and foaled on pasture.
These are ranch mares, not show mares and I did not pay a stud fee. I own the one stallion and borrowed (leased) the other that I pasture bred. He has never been hand bred and I was not sure he would hand breed so I just turned him out like he was used to. Many pasture stallions won't hand breed.
So, the same guidelines do not fit for all situations. Ranches have been pasture breeding forever and ranches have foaled on pasture for generations. Yes, problems can come up. But when you have strong, healthy mares and let them run out on big pastures, don't over-feed them and don't pen them up where they do not get exercise, 99% or more of them will foal and raise a healthy baby with little or no intervention. The two mares and foals I have lost in the last 20 years would have died had I been right there. I had one mare abort a set of twins about 20 years ago.
If you breed show mares and horses that are less hardy than the big, stout ranch mares we keep, you need a lot more management. The more you do that is unnatural, the more you risk a mare. If you are planning on a race or show colt or are paying a high stud fee or are shipping semen, then you obviously need a LOT more management. If you keep mares up and not out on big pastures or feed them too much grain, you are risking them.
When I bred a lot of outside mares, they were palpated for ready follicles, Ultrasounded for twins, and a whole lot more. We did uterine cultures on everything other than maidens, used a lot of heat management with hormones and had 24 hour attendants at foaling time. Boy am I glad I am not doing that any more.
Now that I quit raising NCHA Futurity Sale horses and only raise big, strong, healthy ranch horses that seem to be in great demand for saddle horses, I have gone back to what I did years ago. The horses know how to do it.
I am not going to knock anyone who does not want to do all of the things possible to do at the highest level of management. The value of the mare, the cost of the stud fee and the potential value of the foal will dictate a lot of what should be spent. An older mare and a really valuable mare or a 'fragile' mares should have more management. Otherwise there is not any reason that costs and values should not be taken into consideration.