Nuclear radiation from power plant leaks and bomb tests resulted in millions fewer baby girls born worldwide, according to a new study.

Scientists noted these types of atmospheric blasts rather than on-the-ground incidents like Chernobyl, effected birth gender across the globe.

Scientists at Helmholtz Zentrum München, Germany, analysed population data from 1975 to 2007 for the U.S. and 39 European countries.

There was an increase in the number of baby boys relative to girls in all of the countries from 1964 to 1975. This was the case in many eastern European countries for several years after 1986.

Scientists are putting the first spike down to the atomic bomb tests of the 1960s and 1970s where radioactive atoms were blasted into the atmosphere. Air currents caught these atoms and then distributed them around the world.

They think the second spike is due to the 1986 Chernobyl disaster in which the reactor exploded in the Ukraine.

The effects of Chernobyl were felt locally and no effect was seen in the U.S., probably because it was too far from the disaster to have an effect.

'The closer the country was to Chernobyl, the stronger the effect,' said study co-author Hagen Scherb, a biostatistician at the German Research Center for Environmental Health in Munich.

More males were born relative to females in Belarus - the Ukraine's neighbour - than in France.

The study is based largely on Cold War-era statistics, but the findings are highly relevant for how gender could be effected after future nuclear disasters.

And in the wake of Japan's Fukushima Daiichi nuclear power plant accident experts are predicting another baby boy boom could be imminent, especially on the U.S. West Coast.

Previous radiation experiments on animals may give a clue for the increase in male births. Tests showed that radiation caused damage to the X chromosome in sperm, Dr Scherb said.

A human sperm cell contains either an X or Y chromosome, while an egg only has a X chromosome. An XY combination will become a boy, while an XX combination will be a girl.

(Read by Renee Haines. Renee Haines is a journalist at the China Daily Website.)

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(Agencies)