Report said that a 700 years old royal tomb was discovered near Peking China; along with it is the chart which predicts whether your baby will be boy or girl. The chart is said to have 99% accuracy and have been used by thousand of couples.
I try to find scientific reports to prove this claim, but up to this time I can't find any.
I will not claim for its accuracy, but it is good to know that many have said to try it.