(CNN) — Boy or girl?

A new study says the sex of a baby — may not be decided the way you’ve heard.

Some believe a mother’s likelihood to have boys or girls is decided by their father’s DNA.

Others think the parents’ hormones at the moment of conception have an influence.

But according to a new study published in the medical journal Proceedings of the Royal Society, genetically it all comes down to chance.

Researchers studied the entire population of sweden since 1932, that’s 4.7-million births.

The lead author says the study showed that individuals don’t have an innate tendency to have offspring of one sex or the other instead genetically speaking he says it’s essentially random.

Using information from Swedish birth registries, the researchers compared whether siblings tended to have offspring of the same sex.

their statistical analysis ruled out the possibility that characteristics of the parents influence the likelihood of having boys or girls.

Because of the enormous size of the data used in the study researchers say they’re very confident of the findings.

The study’s lead author says they can’t rule out the possibility that extreme environmental events, like famine, could affect offspring sex ratios but he says researchers can say for sure that the variability of environments in Sweden did not affect sex of the children of those born after 1932.