Boy or girl: Is there a science behind guessing the royal baby's gender?

(CNN) - The countdown to the royal baby is on.

The Duchess of Cambridge is expected to give birth in July, and speculation is rampant about whether she'll have a little prince or a princess -- but is there a science behind the guessing game?

Biologist Fiona Mathews is an expert on the science of sex prediction. She says there is real evidence that the royal couple is likely to have a daughter.

First, there's Catherine's tiny pre-pregnancy waistline. Mathews' own study shows women who eat less are more likely to conceive a girl.

"One idea is that maybe boy babies or boy embryos need to have a much richer food supply," Mathews said.

Then, there are Prince William's daring rescues as a Royal Air Force pilot.

"It's emotional. It's physical. It's very demanding," she said. "Those men are more likely to have girl infants than boys."

Finally, the Duchess has been admitted to hospital after suffering from very severe morning sickness. According to one study, that means she's 80 percent more likely to have a girl.

Of course, it might be too soon to paint the royal nursery pink.

The baby's gender will be revealed by being posted in the Buckingham Palace courtyard, just like when Prince William was born.