Traditionally, women's buttonholes are on the right side of their clothing, while men's buttonholes are on the left side. The most generally accepted reason for this difference dates back to the days when women of leisure were dressed by their servants. The buttonhole placement was designed for the servants' ease.
Another theory of the differing buttonhole placement is that a woman and man, seated by one another in a carriage, could see into one another's shirts. Horizontal buttonholes and proper placement help reduce gaps. For women, one buttonhole should be placed at the fullest part of their bustline with the remaining buttonholes spaced evenly and closely together.