'Great Leighs Church Records
James Olmsted and Jane Bristow, married 12th August, 1576. Baptized: ... Mary, 15th December, 1593; Thomas (twin), 15th December, 1593.'
Assuming these were the children of James and Jane (Bristow) Olmsted (as appears to be the author's assumption), and that the baptism date of the next oldest child (John) was in Feb 1592/3 (as given by this author) and not 1591/2, these twins were likely very premature. The fact that Thomas was named the same as a living sibling, and the likelihood that the twins were premature suggest that the twins were stillborn. I have seen other parish registers (in Norway) where stillborn children were listed along with baptisms. If this is the case, the burial record for Mary Olmsted in Dec 1594 was for the older sibling Mary, meaning that both twins were named the same as living siblings. This is how I have chosen to interpret the data.