A brief addendum to iain's write-up:
Joanna Southcott made her announcement that she was pregnant with an immaculately conceived messiah named Shiloh when she was 64 years old. She died a few months later.
In accordance with her last wishes, her body was kept warm for four days and four nights before being dissected to ascertain the truth of her claim to pregnancy. The results of the dissection: no baby, and no established cause of death. The appearance of the pregnancy was determined to be the effect of extreme flatulence and "extensive omental fat".