Lol, I was frantically searching the internet for "premature foals" 2 years ago as I was afraid she was going to go too soon. She actually hung on a few weeks longer than I thought but still quite early at 328 days. Perfectly healthy foal (the black one in my siggy) but blew the theory of mares always carrying the same length because the bay was born at 360+ the year before!
Both colts, I was delighted she was going early the second time because I was sure it was a filly.
We are at 322 now and a few days ago I thought she was going to go within the week but no change now for the last 4 days so I think / hope she is going to hang on till the weathers a bit better!
If i remenber rightly, one breeder on here has a mare who routinely foals at 315 or 318 (can't remember which) but any sooner than this and baby would probably need special care.
