Occupations that involve stress or pollutants seem to lead to more girls.

56 per cent of the women who had the highest energy intake had boys.

45 per cent of the women who had the lowest energy intake had boys.

Remember, whether you're having a boy or a girl, a healthy diet is very important before and during pregnancy.

Some studies have looked at the father's occupation and the ratio of boys and girls.

This may be linked to a higher chance of having a girl.

A study divided 740 British women into groups according to their calorie intake.

So by having infrequent sex, you are less likely to have sex close to the time you ovulate.

That means that a longer-lasting female sperm is more likely to win the race.

This may lead to changes in the egg, which makes it easier for male sperm to penetrate.

Just how this happens no one is sure, but there is much mystery still about the moment of conception.

Male sperm and embryos are acknowledged to be more fragile and it may be that they are more affected by mothers catching infections.