The added rule about centuries (versus just every four years) was an additional fix to make up for the fact that an extra day every four years is too much of a correction.
The chances of having a leap birthday are one in 1,461.
Despite the fact that almost a third of women said they would be worried about their partner's reaction.
However, more than half of men (59 per cent) would love their girlfriends to get down on one knee.
Yet just 15 per cent of women said they would consider proposing.
Although there's a theory that most unmarried men would love for their female partners to propose, recent research suggests Leap Year-inspired betrothals are doomed to failure.
As an earth year is not exactly 365.25 days long Pope Gregory XIII's astronomers decided to lose three days every 400 years when they introduced the Gregorian calendar in 1582.
So February lost out to August in the battle of the extra days.
Some suggest those born before midday on February 29 should celebrate their birthdays on February 28, while those born in the afternoon and evening of the 28th should celebrate their special day on March 1 (St David's Day).
About 4.1 million people around the world have been born on the 29th.
St Patrick then supposedly gave women the chance to ask the question every four years.
The tradition is not thought to have become commonplace until the 19th Century.
The truth behind this tale is dubious at best - after all Queen Margaret was just eight years old when she died and scholars have been unable to find a record of the law.