The living arrangements of parents at the time a baby is conceived may play a role in determining its sex, research suggests.

A US study found parents who were married or living together before conception were slightly more likely to have a boy than those who were not.

The study, by the US National Bureau of Economic Research, is based on data from 86,436 births.

Details are published in Proceedings of The Royal Society.

Overall, the study found that 51.5% of babies born to couples living together at the time of conception were boys, compared to 49.9% among parents who were not.

Although this might seem like a small difference, it is actually statistically highly significant when considered across a whole population.

When the researchers looked at brothers and sisters, they found that couples who were living together before conception were 14% more likely to have a male child than when they were not.

The researchers say their finding could explain the fall in the proportion of male births in some developed countries over the past 30 years.

More here.