A study by Dutch scientists have found that women's choice of diet influences the sex of the child.
They found that women could increase their chances of giving birth to a girl by consuming food with high levels of calcium and magnesium, such as green vegetables, in the weeks before conception.
Of a group of women who followed a diet drawn up by the researchers, 80 per cent went on to have daughters.
By contrast, foods rich in potassium and sodium - such as bananas and potatoes - would be likely to help women who want to have sons, although this has yet to be tested.
The researchers are convinced that following the right diet can help couples increase their chances of choosing the sex of their child, although they don't know the exact role played by other factors such as the timing of conception.
They spent five years working with 172 couples, all of whom wanted to add girls to their families - between them they already had 358 sons and just two daughters.
Each began a diet rich in fruit, vegetables and rice in the nine weeks before they planned to attempt to conceive to increase the levels of calcium and magnesium in their bloodstream.
In addition, they were given daily tablets of the key minerals, had regular blood monitoring and had to learn as accurately as possible their moment of peak fertility each month.
At the end of the trial, out of 32 couples who completed the programme, 26 mothers gave birth to girls and only six had boys.
"People now know that if they do everything we have suggested, their chances of having a girl will improve dramatically," the Daily Mail quoted Annet Noorlander, a biologist with firm Gender Consult, as saying.
"This method is experimental, but we have proved it works."
Her company carried out the research with teams from Delft and Maastricht universities.
The study has been reported in the journal Reproductive BioMedicine Online.